Plant Diversity Taxonomy

PlantDiversity

Ethnobotany

Forestry

Horticulture

Photosynthesis and Respiration

Plant Biotechnology

Plant Cells and Tissues

Plant Development

Plant Diversity

Plant Ecology

Plant Genetics

Plant Nutrition

PlantDiversity

J. Phil Gibson and terri r. Gibson

Series Editor William G. Hopkins

Professor Emeritus of Biologyuniversity of Western ontario

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Introduction vii

1 The Diversity of Plant Life 2

2 The History of Plant Systematics 18

3 Fungi and Algae 32

4 Seedless Nonvascular Plants The Bryophytes 50

5 Seedless Vascular Plants 62

6 Nonflowering Seed Plants The Gymnosperms 78

7 Flowering Plants The Angiosperms 94

Glossary 112

Bibliography 123 FurtherReading 125 Index 129

By William G. Hopkins

vii

“Have you thanked a green plant today?” reads a popular bumper sticker.Indeedweshouldthankgreenplantsforprovidingthefoodweeat,fiberfortheclothingwewear,woodforbuildingourhouses,andtheoxygenwebreathe.Withoutplants,humansandotheranimalssimplycouldnotexist.Psycholo-giststellusthatplantsalsoprovideasenseofwell-beingandpeaceofmind,whichiswhywepreserveforestedparksinourcities,surroundourhomeswithgardens,andinstallplantsandflowersinourhomesandworkplaces.Giftsofflowersarethemostpopularwaytoacknowledgeweddings,funerals,andothereventsofpassage. GardeningisoneofthefastestgrowinghobbiesinNorthAmericaandtheproductionofornamentalplantscontributesbillionsofdollarsannuallytotheeconomy.

Humanhistoryhasbeenstronglyinfluencedbyplants.Theriseofagri-cultureintheFertileCrescentofMesopotamiabroughtpreviouslyscatteredhunter-gathererstogetherintovillages.Eversince,theavailabilityoflandandwaterforcultivatingplantshasbeenamajorfactorindeterminingthelocationofhumansettlements.Worldexplorationanddiscoverywasdrivenbythesearchforherbsandspices.ThecultivationofNewWorldcrops—sugar,

viii introduction

cotton, and tobacco—was responsible for the introductionof slavery toAmerica,thehumanandsocialconsequencesofwhicharestillwithus.ThepushwestwardbyEnglishcolonistsintotherichlandsoftheOhioRivervalleyinthemid-1700swasdrivenbytheneedtoincreasecornproductionandwasafactorinprecipitatingtheFrenchandIndianWar.TheIrishpotatofaminein1847setinmotionawaveofmigration,mostlytoNorthAmerica,thatwouldreducethepopulationofIrelandbyhalfoverthenext50years.

Asayounguniversityinstructordirectingbiologytutorialsinaclassroomthatlookedoutoverawoodedarea,Iwouldaskeachgroupofstudentstolookoutthewindowandtellmewhattheysaw.Moreoftenthannotthequestionwouldbemetwithablank,questioninglook.Plantsaresomuchapartofourenvironmentandthefabricofoureverydaylivesthattheyrarelyregisterinourconsciousthought.Yettoday,facedwithdisappearingrainforests,explodingpopulationgrowth,urbansprawl,andconcernsaboutclimatechange,theproductivecapacityofglobalagriculturalandforestryecosystemsisputunder increasingpressure.Understandingplants isevenmoreessentialasweattempttobuildasustainableenvironmentforthefuture.

TheGreenWorldseriesopensdoorstotheworldofplants.Theseriesdescribeswhatplantsare,whatplantsdo,andwhereplants fit into theoverallschemeofthings.Plant Diversity introducesustotheseeminglyendlessvarietyinplantlife,fromthesmallestalgatothetallesttrees.Wealsolearnthesignificanceofplantdiversityinplanetaryecosystemsandwhy understanding and protecting this diversity is critical to our ownhealthandsurvival.

2

TheDiversityofPlantLife

It is my pleasure here to take Botany as my special study,which previously was the knowledge of a few plants;today however the abundance of material for choicehas made it the most extensive of all the sciences.

—Carolus Linnaeus (1707–1778)from the preface of Species Plantarum, 1753

Plants can be found nearly everywhere on Earth. They live in thecracksofNewYorkCitysidewalks.TheysurviveinthesandsoftheSahara.TheythriveinthejunglesoftheAmazonbasin.Theplantsthemselvesarenolessdiversethantheirsurround-ings, coming in all different colors, sizes, shapes, and scents(Figure1.1).Someplants,suchasannualbluegrass(Poa annua)andpoolsprite(Amphianthus pusillus),completetheirlifecycleinamatterofweeks,whereasindividualsofotherspecies,suchasbristleconepine(Pinus longaeva),canlivehundredsoreventhousandsofyears.Thesediversefeaturesnotonlyindicatetheability of plants to adapt to their environment, they also givecluestotheevolutionaryhistoryofplantsandinsightsintothehistoryoflifeonEarth.

TheVaLueoFPLanTDIVeRsITyKnowledgeandappreciationofplantdiversityhasalwaysplayedavitalroleinhumansurvival.Fortheearliesthunter-gatherers,itwasessential toknowwhichplantswereedibleandwhichwerenot.Carelesslyeatingthewrongkindofleaf,fruit,orseedcouldcausesicknessorevendeath.Asculturesdeveloped,earlyhumanslearnednotonlywhichplantstoeat,butalsowhichplants provided materials for housing, clothing, tools, anddyes. Plants such as sacred lotus (Nelumbo nucifera), peyote(Lophophora williamsii), and even cacao (Theobroma cacao), theplantfromwhichchocolateismade,wereusedinreligiousceremonies.Humansalsolearnedwhichplantshadmedicinalproperties.Individualswhoknewwhichplantstouse,wheretofindthem,andhowtopreparethemwereheldinhighregardasshamans,medicinemen,orhealerswhoseskillcouldmeanthedifferencebetweenlifeanddeathfortheirpeople.

Today,peoplestilldependonplantsfortheirsurvival.Plantsmakeupa significantportionof thedietof themore than6billionpeopleonthisplanet.Plantsprovidelumberandotherconstruction materials for housing. They provide fibers for

4

TheDiversityofPlantLife

5the diversity of Plant Life

Figure 1.1 Plants display a wide variety of forms. Photographed above are pine cones in a cluster (a), ferns found in the Bialowieza Forest in Poland (b), a cholla cactus (c), and a bouquet of pink tulips (d ).

a b

c d

6 Plant diversity

clothingandotheritems.Billionsofdollarsarespentannuallyonornamentalplantsandflowers.Eventhemodernpharmaceu-tical industrycontinuestodependonplants,withmorethan25% of prescription drugs containing compounds extractedfromplants.

Inadditiontobeingusefultohumans,plantdiversityisalsoimportant to the functioning of planetary ecological systems.Plantsdirectthecyclingofnutrientsbetweenthesoilandotherlivingorganisms.Throughphotosynthesis,plantsconvertenergyfromthesunintootherformsofenergythatnonphotosyntheticorganisms,suchashumansandotheranimals,canuse.Plantsregulate temperature, influenceprecipitationpatterns,providehabitatforotherorganisms,andperformmanyotheressentialecologicalprocesses.

Unfortunately, many human activities, particularly habitatdestruction,continuetohaveanegativeimpactonplantdiver-sity worldwide. Development of effective conservation strate-gies to protect botanical resources will depend greatly uponknowledgeofplantdiversityanditsecologicalimportance.Thus,appreciatingandunderstandingplantdiversityiscriticalforthesurvivalandqualityofalllifeonEarth.

EthnobotanyResearchers estimate that more than 80% of the world’s population still depends directly on plants for herbal medicines. Ethnobotanists are scientists who study the ways in which indigenous peoples use plants, par-ticularly for medicinal purposes. Many botanists, ethnobotanists, anthropol-ogists, and biochemists are currently working with native peoples around the world to learn about medicinal uses of different plants to preserve cultural traditions and knowledge. In the past, many medicines have been developed from plants used for healing purposes by tribal peoples.


ThesTuDyoFBIoLoGIcaLanDBoTanIcaLDIVeRsITyThebranchofbiologythatstudiesbiodiversity isknownassystem-

atics.Itismadeupofthreesubdisciplines:taxonomy,classification,andphylogeny.

Taxonomy is the process of naming individual plants orgroupsofplants.Aplantoftenhastwonames:acommon nameand a scientific name. Common names are given to plantsby the people who live near them. Sunflower, loblolly pine,cottonwood, and crabapple are examples of common namesfrequently used by scientists and nonscientists alike. Com-monnamesareofteneasytorememberandarefamiliartothegeneralpopulation.

Common names often describe some aspect of a plant’sphysicalappearance.Nameslikepitcherplant,cat’sclaw,fishon a line, or leafy elephant foot conjure images familiar toeveryone. Common names sometimes suggest a plant’s uses(broomstraw,matchweed,scouringrush)orwarnofitsdan-gers(stingingnettle,poisonivy,deathcamas).However,thisisnotalwaysthecase.Thenameshenbit,dogwood,andrattle-snakemasterarecolorful,butgivelittleinformationabouttheplantitself.

Aplantmayhavemorethanonecommonname.Forexample,waxgoldenweedandSpanishgoldbothrefertothesameplantspecies,Grindelia ciliata.Acommonnamemayrefertoseveralplantswithsimilarcharacteristics.Aquacatillo(“littleavocado”),forexample,isacommonnamethatidentifiesseveraldifferenttropicaltreespeciesthatproducesmallavocados.Consequently,commonnamescanbeaproblemforscientistsbecausetheyarenot necessarily specific to a single plant, there are no rules togoverntheirapplication,andtheyprovidelimitedinformationaboutaplantoritscharacteristics.

In the 1700s, a Swedish botanist named Carolus Linnaeus(1701–1778)reducedthepolynomial(manyname)systemtoabi-nomialsystem.Scientistscurrentlyusethisbinomial nomenclature

8 Plant diversity

(twoname)systemofscientificorLatinnamestoidentifyspe-cies.Forexample,thescientificnamefortheEuropeangrapeisVitis vinifera. Thefirstpartofthename(Vitis)isthegenus andthesecondpart(vinifera) is thespecies.Agenusnamecanbeusedalonetorefertoallmembersofagenus,butspeciesnamesareneverusedalone.

TheuseofscientificnamesforplantsisbaseduponasetofrulescalledtheInternational Code of Botanical Nomenclature (ICBN).AllnamesareinLatinorhavebeenLatinizedregardlessofaplant’slocation, its possible uses, or any associations with a particularculture. Latinwaschosenbecausethiswasthe languageoftheclassical works of botany and other sciences. Scientists aroundtheworldcancommunicatewithcertaintyaboutaspecificplant,regardlessofthelanguagetheythemselvesspeak.ThefollowingaresomeofthefundamentalICBNrules:

1. Aplantorgroupofplantscanhaveonlyonevalidname.

2. Thevalidnameforaspeciesistheonefirstpublishedclos-

esttothedateMay1,1753(thepublicationdateforCaro-

lusLinnaeus’bookSpecies Plantarum, whichisconsidered

thestartingpointformoderntaxonomy).

3. Anameisvalidifithasbeenpublishedinscientificlitera-

tureandcontainsacompletedescriptionoftheplantwrit-

teninLatin.

4. Avalidnameforaspeciesconsistsoftwoparts,agenusname

andaspeciesname.Thesetwopartsmaynotbethesame.

5. Agenusnamecanbeusedonlyonce,butaparticularspe-

ciesnamecanbeusedincombinationwithdifferentgenera.

Forexample,Carya glabra (pignuthickory)andRhus glabra

(smoothsumac)havethesamespeciesnameglabra(mean-

ing“withouthairs”),buttheyaretwodifferentspecies.

6. Thegenusandspeciesnamesareitalicizedorunderlined.

9the diversity of Plant Life 9

7. Thebotanicalrulesofnomenclatureareindependentof

therulesthatgovernnamingofotherorganisms.

TherearemanyotherrulesintheICBNthatgiveordertotheprocessofnaming.Botanistsfromaroundtheworldmeetevery

Families With two namesAlthough the ICBN states that there can be only one correct name for any group, there is an exception to this rule. Eight plant families have two cor-rect, accepted names. The modern names have endings consistent with the ICBN rules. The older names deviate from ICBN rules, but have been in use for so many years (centuries, in some instances) that many botanists still use them today.

Table1.1 Plant Families With Two Valid Scientific Names

ICBN name Older name Common name

Apiaceae Umbelliferae Parsleyfamily

Arecaceae Palmae Palmfamily

Asteraceae Compositae Sunflowerfamily

Brassicaceae Cruciferae Mustardfamily

Clusiaceae Guttiferae Garciniafamily

Fabaceae Leguminosae Beanfamily

Lamiaceae Labiatae Mintfamily

Poaceae Gramineae Grassfamily

10 Plant diversity

fiveyearsatthe International Botanical Congress todiscussrules,propose changes, and make sure that the ICBN is serving theneedsofthebotanicalcommunity.

Thesecondpartofsystematics,classification,istheprocessofgroupingnamedorganismsintoanorderedsystem.Smallergroups are placed together into progressively larger groups,likeaseriesofnestingboxes.Inmodernclassificationsystems,thelargest,mostinclusivegroupingisthekingdom (allplantsareintheKingdomPlantae).Plantsarethendividedintosuc-cessively smaller groups, the smallest, and least inclusive ofwhichisthespecies.Aspeciesisaparticularkindoforganismthattypicallycanreproducewithothermembersofthesame

Table1.2 International Code of Botanical Nomenclature Endings

Taxonomic Level ICBN ending Scientific name

Kingdom -ae Plantae

Division -phyta Embryophyta

Class -opsida Angiospermopsida

Subclass -idae Asteridae

Order -ales Asterales

Family -aceae Asteraceae

Genus Grindelia

Species Grindelia lanceolata

CommonName narrowleafgumweed


speciesandcanbedistinguishedfromotherspeciesbasedona number of different characteristics. Members of the samespeciesallshareanevolutionaryhistorydistinctfromthatofotherspecies.

The ICBN dictates specific endings for names at the dif-ferent levels of plant classification (Table 1.2). For example,allplantfamilynamesendwiththesuffix-aceae.Orders,theclassification level above family, end in -ales. Through thissystem,botanistscanquicklyrecognizethetaxonomiclevelofanyname.

Thefinalcomponentofsystematicsisthestudyofphylog-eny,theevolutionaryrelationshipamongorganisms.Throughthis type of research, systematists can show how organismsevolved,howdifferentorganismsare evolutionarily related tooneanother,andhowdifferentgroupshavedivergedanddif-ferentiatedfromoneanotherthroughouttime.Studiesofphy-logenyoftenresultintheconstructionofdendrograms,whicharebranchingdiagramsthatshowtheevolutionaryfamilytreeforagroup.

sIxKInGDomsoFLIFeAlthoughtherearedifferencesofopinion,mostbiologistsrecog-nizesixkingdoms:Bacteria, Archaea, Protista, Animalia, Fungi, and

taxonomic AbbreviationsSystematists have developed their own terms and shorthand abbreviations to refer to different taxonomic groupings. One of the most commonly used words is taxon (pl. taxa), which refers to a group at any classification level. Genus names can be used alone or followed by the abbreviations sp. or spp., which are abbreviations for the word species (sp. refers to a single species and spp. refers to multiple species).

12 Plant diversity

Plantae. Organismsareplacedintooneofthesekingdoms basedupontheirgeneticandcellularfeatures,aswellastheirmodesofobtainingnutrientsandenergy.

KingdomsEubacteriaandArchaeacontaindescendantsofthe oldest organisms on Earth. Members of these two king-domsareprokaryotic,meaningthattheircellslackanucleus andmembrane-bound organelles within them. Kingdom Bacteriais very diverse and contains a majority of the prokaryoticorganisms on Earth. This group includes the true bacteriaand cyanobacteria (blue-green algae). Kingdom Archaea isanotherdiversegroup.Manymembersofthiskingdomoftenlive inharshenvironments,suchashotspringsanddeepseathermalvents,inconditionssimilartothosefoundinEarth’searlyhistory.

The remaining four kingdoms are eukaryotic, meaning thattheircellscontainanucleusandmembrane-boundorganelles.Kingdom Protista contains many unicellular organisms andsimple multicellular organisms. Kingdom Protista containsorganismsthatsharesimilaritieswithanimals,fungi,andplants.Ofparticularimportancearethegreenalgae,whichplayedanimportantroleintheevolutionofplants.

KingdomsAnimaliaandFungicontainmulticellular,eukary-oticorganismsthatareheterotrophs; theymustconsumeotherorganisms to obtain the nutrition and energy they need tolive.Animalsingesttheorganismstheyfeeduponandsecreteenzymes that break down their food into simple molecules,whichareabsorbedbytissuesofthedigestivesystem.Incon-trast, fungi secrete enzymesonto their food source, and thenabsorb the digested food from the environment. Fungi werelongconsideredplants.Cellularandmoleculardata,however,haveshownconclusivelythatfungiarenotplantsandshouldbeplacedinaseparatekingdom.Interestingly,geneticdatahaveshown that fungiareactuallymoreclosely related toanimalsthantoplants.


Kingdom Plantae contains organisms that are autotrophs,

which means that they are capable of producing their ownenergy.Botanistshaveidentifiedmorethan300,000differentspecies of plants; there may be as many as 500,000 differentplant species on Earth. Plants are divided into four majorgroups: bryophytes, seedless vascular plants, gymnosperms, andangiosperms.

WhaTIsaPLanT?Likeall living things,plantsarecomposedofcells,useenergyandnutrientsintheirmetabolism,andhaveevolvedavarietyofadaptationsthathelpthemsurviveintheirenvironment.Plantsalso reproduce and interact with other living things. Severaluniquefeatures,however,makeitpossibletogrouptheseorgan-ismsintotheirownkingdom.

Avastmajorityofplantsarephotoautotrophs. Theyconductthebiochemicalprocessofphotosynthesis in structurescalled

chloroplasts (Figure1.2). Throughphotosynthesis,plants convertenergyinsunlightintochemicalformsofenergy,suchassugarsandstarch,thattheycanthenusetomeettheirownneedsandprovideenergytootherlivingthings.Plantsconductphotosyn-thesisusinguniquecombinationsofdifferentpigments,suchaschlorophyll a,chlorophyll b, and carotenoids. Somephotosyntheticbacteriacontainchlorophyllb,butonlyplantsandgreenalgaecontain theotherphotosyntheticpigments. It isworthnotingthatthereareparasiticplants,suchasdwarfmistletoes(Arceu-thobium) and Indian pipe (Monotropa uniflora), that do notproducephotosyntheticpigmentsandarenotphotosynthetic;despite this, theirbiologyandothertraitsclearly indicate thattheyareplants.

Theplantcellwallisanotheruniquefeatureoftheseorgan-isms. Plant cells are surrounded by a wall made of complexcarbohydrates,suchascelluloseorlignin,whichprovidesrigidityandstructuralsupportfortheplantbody.

14 Plant diversity

Anotherdefiningtraitofplantsisthatthestructuresinwhichgametes(eggsandsperm)areproducedaresurroundedbyalayerof cells called the sterile jacket, which protects the developinggametes.Furthermore,theplanteggisnotcapableofmovementandthusremainsinfemalegametophytetissues.

Figure 1.2 Plant cells are made out of many components, including a nucleus, cell wall, and chloroplasts.


TheaLTeRnaTIonoFGeneRaTIons

Alllivingthingshavealifecycle.Themostfamiliarlifecycletomostpeopleisthatofanimals,inwhichsingle-celledgam-etes unite during sexual reproduction to form a multicellularzygote that grows and develops into a mature adult. Gam-etes are haploid (contain one complete set of chromosomes).Zygotesandadultsarediploid (contain twocomplete setsofchromosomes).Haploidcellsareproducedwhendiploidcellsundergotheprocessofmeiosis, dividingtwicetoproducefourhaploidcells.Mitosisis asimilarprocess, butinsteadofhalv-ingthegeneticmaterialinthecell,itproducestwoidenticalcellswiththesameamountofgeneticmaterialastheoriginalparentcell.

Plants go through haploid and diploid phases in the lifecycle.Thisunique typeof lifecycle is called thealternation of

generations because during sexual reproduction there is analternationbetweenamulticellularhaploidgenerationcalledthe gametophyte and a multicellular diploid generation calledthe sporophyte (Figure 1.3). The gametophyte is a plant thatproduces gametes. Through fertilization, the egg and spermunite to form a zygote that becomes the diploid sporophyte.Thesporophyteisaplantthatproducesspores.Thesporophytegrowsthroughmitosis.Eventually,specialcellsinitsreproduc-tivetissues(spore mother cells) undergomeiosistoformhaploidspores.Thesporesgerminatetoformthegametophyte,andthecyclerepeatsitself.

Thealternationofgenerations is important in thestudyofplant diversity because the four major groups of plants differwith regard to which generation, gametophyte or sporophyte,dominatesthelifecycle.Inbryophytes,forexample,thegameto-phyteisthedominantgeneration,whereasthesporophyteisthedominantgenerationinangiosperms.

16 Plant diversity

summaRy

PlantsareanimportantcomponentoflifeonEarth.Theypro-videavarietyofecologicalservicesrangingfromtheproductionoffoodthroughphotosynthesistoprovidinghabitatsforotherlivingthings.Plantsalsoprovideamultitudeofnaturalresourcesforhumansandhaveperformedimportantrolesintheevolutionofhumansandthegrowthofhumanculturesandpopulations.

Figure 1.3 Plants alternate between sporophyte and gametophyte phases. Sporophytes undergo meiosis to form spores, which initiates the gametophyte phase. Gametophytes have half the number of chro-mosomes as sporophytes. Male and female gametophytes, or gametes, combine during fertilization. The result of fertilization is the formation of a zygote.


Throughsystematics,botanistsidentifyandorganizethediver-sityofplantlifenotonlytocataloguebotanicaldiversity,butalsotounderstanditsoriginsandevolutionaryhistory.

1818

ThehistoryofPlantsystematics


The botanist is he who can affix similar names tosimilar vegetables, and different names to different ones,

so as to be intelligible to every one—Carolus Linnaeus

20 Plant diversity

20

The earliest efforts to categorize plants were based on their usefulness to humans. Ancient texts and records describingmedicinal,agricultural,andotherusesofplantshavesurvivedfromculturesaroundtheworld.Oneoftheoldestsuchbookswaswrittenmorethan4,500yearsagobyEmperorChi'enNungofChina.Onethousandyearslater,anunknownauthorwrotetheEberspapyrus,ascrollthatdescribedthepharmacologicalusesofplantsfoundinancientEgypt.

Morethan2,300yearsago,theGreeknaturalistTheophrastus wroteaboutthecultivationandusesofvariousplants,organizingthemintogroupsbasedoncharacteristicssuchastheirgrowthform (herb, tree, or shrub), fruit, and leaves. He gathered muchoftheinformationforhisbookHistoria Plantarum (HistoryofPlants)bystudyingthegardensofAthens.Heeventuallyestab-lishedthefirstknownbotanicalgarden.

RomannaturalistPlinytheElder(a.d.23–79)describedthehorticulturalandmedicinalusesofmanyplantsinhisbookHis-toria Naturalis (NaturalHistory).Dioscorides(circaa.d. 40–90),aGreekphysicianinNero’sarmy,wroteDe Materia Medica (TheMaterialofMedicine),abookthatclassifiedanddescribedmorethan600plants.NotonlydidDe Materia Medicacontainwrittendescriptions,itwasalsothefirstbotanybooktoincludeillustra-tions.Thisbookwasoneof theprimarymedicalreferences inEuropeuntilthe1600s.

OnethousandyearsafterPlinyandDioscorides,aChinesephy-siciannamedTangShen-weipublishedCheng Lei Pen Ts’ao (TheMaterialsofMedicineArrangedAccordingtoPattern).Firstpub-lishedin1108,thisclassicworkofEasternmedicinewentthrough12editionsandwaseventranslatedandpublishedinJapanin1625.

TheReBIRThoFBoTanyIn Europe, botany—like other sciences—lay mostly dormantuntil the Renaissance. The renewed interest at this time coin-cidedwiththeinventionoftheprintingpress,whichusheredintheso-calledAgeofHerbals.Forthefirsttime,leadingGerman


21the History of Plant Systematics

botanists,suchasOttoBrunfels,HieronymusBock,andLeonartFuchs,wereabletopublishandwidelydistributebooksthathaddescriptionsandpicturesofplants(Figure2.1).

The firstuniversities inUpper ItalyandEuropeestablishedbotanicalgardenstostudyliveplants.LucaGhini(1490–1556),working at the University of Pisa, invented the process of

Figure 2.1 Herbals are books that describe the many characteristics of plants used in herbal medicines. This illustration of a peony is from an herbal published in 1613.

22 Plant diversity

collecting,pressing,anddryingplantstocreatethefirstherbarium,alibraryofpreservedplantmaterials.Theherbariumestablishedin1532byGhini’sstudentGherhardsCibo(1512–1597)istheoldeststillinexistence.

Althoughresearcherscontinuedtofocusonthemedicinalusesofplants,botanistsof theseventeenthcenturybeganto investi-gateotherareas,aswell.Theirdiscoveriesledtothedevelopmentof thefirstclassificationsystemsbasedonfeaturesof theplantsratherthantheiruses.Naturalists,suchasJohnRay(1628–1705)andPierreMagnol(1638–1715),describedandnamednumerousEuropeanandAsianspecies,genera,andfamilies.Thesebotanistsandothersbegantoclarifyconceptsaboutplantfamiliesandgen-erathatwouldbecomethefoundationofmodernsystematics.

caRoLusLInnaeusBytheeighteenthcentury,botanistshadcollected,stored,stud-ied,andclassifiedagreatdealofplantmaterialfromaroundtheworld.Therewasnostandardizedsystemorconsensus,however,abouthowtonameaplant—oranyotherkindoforganism,forthatmatter.This ledtoapolynomialsystemthatwascumber-someandimpractical.Forexample,thefullnameforoneplantspecies was Serratula foliis ovato-oblingis accuminatus serratis,

What is an Herbarium?An herbarium is a library of pressed and dried plants. In the herbarium, dried whole plants or parts of plants are mounted on pieces of paper called herbarium sheets. Each sheet has a label that identifies the plant and tells where and when the specimen was collected and by whom. Many professional systematists work at herbaria associated with botanical gardens, colleges, or universities. Specimens collected by Linnaeus are in herbarium collections around the world.


floribus corymbosis, calcybus subrotundis. When the binomialsystem(seeChapter1)wasintroducedbyCarolusLinnaeus,thiswasshortenedtoSerratula glauca.

InSpecies Plantarum,publishedMay1,1753,Linnaeusgavebinomialnamestomorethan7,300species(Figure2.2).Althoughhe was not the first person to consider a simplified binomialsystem, Linnaeus was the first to develop and consistently useaworkablenamingsystem—onethathasbeeninuseformorethan200years.

naTuRaLcLassIFIcaTIonsysTemsanDeVoLuTIonAlthough his binomial system was successful, Linnaeus’s clas-sification system was not widely accepted. Linnaeus catego-rizedplantsbasedonthenumberandarrangementofstamens,and then subdivided them using other floral traits. This arbi-traryapproachproducedanartificial classification system,whichgroupedunrelatedspeciestogether.

ContemporariesofLinnaeus,suchasMichelAdanson(1727–1806)andAntoineLaurentdeJussieu(1748–1836),preferredtouseamultitudeofdifferentfeatures(forexample,flowers,fruits,andleaves)togroupplantsbasedonoverallsimilarity.Usingthisapproach, De Jussieu described more than 100 plant families,manyofwhichthatarestillrecognizedtoday.

Famous Botanists rememberedScientists often recognize individuals who have made major contributions to the field of botany by naming plants after them. The genus Magnolia is named after the botanist Pierre Magnol, whose work developed the concept of plant families. The genus Dioscorea (yams) is named in honor of the Greek botanist Dioscorides. Several paintings show Linnaeus wearing or holding a small cluster of Linnaea flowers, a genus that was named after him.

24 Plant diversity

Figure 2.2 Carolus Linnaeus is known for his contributions to modern taxonomy. This famous picture of Linnaeus in Lapland dress shows him holding a cluster of flowers named after him, Linnaea borealis.


De Jussieu was one of the first botanists to group relatedspecies and families together. This approach produced a natu-

ral classification system that reflectedevolutionaryrelationshipsamongplants.Thegoalofproducingnaturalclassificationswasfurtherenhancedwiththepublicationof The Origin of Species in1859. In this groundbreakingbook,CharlesDarwin describedhowspeciesevolveandhowadaptationsandothertraitsspreadthroughtheprocessofnatural selection.Naturalselectionoccurswhenorganismshavetraitsthathelpthemsurvivebetterorpro-ducemoreoffspringthanthosethatlackthosetraits.Throughgreatersurvivalandoffspringproduction,organismswithadap-tivetraitsleavemoredescendants,andtheadaptationbecomesmoreprevalentinfuturegenerations.Withhistheoryofevolu-tion,Darwinshowedthatthediversityoflifecouldbeinterpretedasafamilytree,orgenealogy,thatrevealshowtaxahavechangedthroughouttime.

eVoLuTIon-BaseDcLassIFIcaTIonsAsthetheoryofevolutionspread,botanistsquicklydevelopedevolution-basedclassifications.Prominentbotanists,suchasA.P.deCandolle(1778–1873)inSweden;GeorgeBentham(1800–1884)andSir JosephHooker(1817–1911) inEngland;AugustWilhelm Eichler (1839–1887), Adolf Engler (1844–1930), andKarlPrantl(1849–1893)inGermany;andAsaGray(1810–1888)andCharlesBessey(1845–1915)intheUnitedStates,developedclassificationsystemsinwhichtheyconsideredtheevolutionaryhistory of specific traits. Some general rules they followed indevelopingevolution-basedclassificationsincluded:

• Flowerswithmanyparts(forexample,manystamensor

carpels)arelessadvancedthanflowerswithfewerparts.

• Plantswithwoodystemsaremoreprimitivethanherba-

ceousplants.

26 Plant diversity

• Specieswithflowerscontainingmaleandfemalestructures

arelessadvancedthanspecieswithflowersthatcontainonly

maleoronlyfemaleparts.

Thisnewevolutionaryperspectivegaverisetomodernclas-sificationsthatshowthephylogenyorevolutionaryhistoryandrelationships among organisms in a lineage. Researchers con-tinuetodevelopclassificationsthatdisplaytheevolutionofdif-ferentplantgroups.

moDeRncLassIFIcaTIonsArthurCronquist(1919–1992),LedyardStebbins(1906–2000),andRobertThorne(b.1920)oftheUnitedStates;ArmenTakhta-jan (b. 1910) of the former Soviet Union; and Rolf Dahlgren(1932–1987)ofDenmarkproducedmajorclassificationsystemsforangiospermsthatinfluencedmodernthinkingonfloweringplantevolution.Currently,systematistsworkinginmanydifferentlaboratoriesandherbariatakepartininternationalcollaborativeefforts,suchastheAngiospermPhylogenyGroupandtheTreeofLifeProject.ThesegroupsseektoclarifyourunderstandingofthehistoryoflifeonEarthbyinvestigatinglarge-scalepatternsofplantevolution.

cLaDIsTIcsanDconsTRucTInGPhyLoGenIesSystematistsconstructphylogeniesusinganapproachcalledcla-

distics,atermthatcomesfromtheGreekwordforbranch,klados.

the Meaning of theoryEvolution is sometimes discredited as a theory and not a fact. Scientists use the term theory to refer to a collection of unifying principles that explain proven facts and observations. Thus, the theory of evolution is not a guess, but a well-supported scientific explanation for the diversity of life.


Theobjectiveofcladisticsistoproduceanaturalclassificationinwhicheverydescendantofasingleancestorisplacedonthesamebranch (clade)of adendrogram.Whenallof thedescendentsofacommonancestorareplacedinthesameclade,itiscalledamonophyletic group.By identifyingmonophyleticgroups, sys-tematistscandeterminehowspecifictraitsinalineageevolvedthroughouttime.

Foracladisticstudy,systematistsfirstdeterminewhichchar-acteristicsareprimitive(ancestral)andthenwhichareadvanced.For example, Table 2.1 shows five different traits in the fourmajor groups of plants and algae. The presence of a particu-lar trait is amore evolutionarily advancedcondition than theabsenceofa trait.Forexample,plantswithoutvascular tissue

Table2.1 Comparison of Traits Between Algae and Major Green Plant Groups

Seedless vascular Gymno- Angio- Trait Algae Bryophytes plants sperms sperms

Presence of chlorophylls yes yes yes yes yes a and b

Sterile jacket layer around no yes yes yes yes antheridia and archegonia

Vascular tissue no no yes yes yes

Seeds no no no yes yes

Flowers no no no no yes

28 Plant diversity

(xylemandphloem)appearinthefossilrecordbeforeplantswithvasculartissue.Therefore,theabsenceofvasculartissueinagroupofplantsisamoreprimitiveconditionthanthepresenceofvascu-lartissue.Cladistsusethepatternsofhowadvancedtraitsarisetodetermineevolutionaryrelationshipsamongmembersofalineage.

The data in Table 2.1 can be used to produce a cladogram(Figure2.3)thatdescribesthephylogenyforthemajorgroups

Figure 2.3 The above cladogram shows the relationship among major plant groups.


ofplants.Thiscladogramshowsthatallplantssharedadistantcommon ancestor with algae. Bryophytes are the oldest plantlineage,followedbytheseedlessvascularplants,gymnosperms,andultimatelytheangiosperms.Systematistsusethebranchingpatternsofacladogramtodeveloptheirclassifications.

TheDaTasysTemaTIsTsuseSystematicshasbeenreferredtoasthefieldofsciencewithnodataofitsown.Insomeways,thatiscorrect.Unlikethephysiolo-gistwhocollectsdataonthemetabolicrates,cycles,andprocessesincells,thegeneticistwhocollectsdataonthesequenceofgenesonachromosome,ortheecologistwhocollectsdataonthesizeanddistributionofpopulations,systematistsdonotcollectanyformofdata thatonecouldspecifically identifyassystematicsdata.Instead,theyusethetechniquesofotherscientificfieldstocollectdatathattheycanthenusetodevelopaclassification.

Intheearlystagesofsystematics,botanistsdependedheavilyonmorphology(theoutwardstructuralappearanceofaplant).Traitssuchasleafshape,fruittype,ornumberofpartsinaflowerareeasytoobserveandcompareamonglivingandfossilplants.Withtheinventionofthemicroscope,botaniststurnedtoanatomy (theinternalcellularstructureofaplant)todevelopclassifications.

Botanical resourcesThere are many resources available for individuals who want to explore the botanical diversity around them. One good resource is a field guide. These books often have pictures and descriptions that make it easy for budding botanists to learn the common plants of an area. More advanced students may require a flora, which typically contains an extensive listing of species that occur in an area. Field guides and floras typically contain dichotomous keys, which help users identify plants by leading them through a series of paired questions.

30 Plant diversity

Figure 2.4 DNA sequencing gels are used by modern-day taxonomists to collect genetic data. Each band represents a single fragment of DNA known as a nucleotide. There are four types of nucleotides, abbreviated G (guanine), T (thymine), A (adenine), and C (cytosine).


The field of systematics is constantly changing as differenttechnologicaladvancesarise.Asinstrumentsandtechniquesforanalysisofplantchemicalextractsimprovedinthe1940s,system-atistsbegantocollectchemicaldatafortheirstudies.Inthe1990s,there were tremendous advances in the ability to extract andsequenceDNAfromplantsandimprovedcomputingabilitytoanalyzedatafromDNA(Figure2.4).Systematistsrapidlyincor-poratedthesenewtechniquesintotheiranalyses.Newtechniquescombinenewdatawithearlierformsofdatatofurtherrefinetheunderstandingofplantevolution.

Thereisevencontinueddiscussionamongplantsystematistsabouthoworganismsshouldbenamedandclassified.Recently,systematistsproposedmovingaway fromtheLinnaeansystemtoward a system called the Phylocode, which has no hierarchi-calrankings,suchasfamilyororder.Instead,itonlyrecognizesclades.Although there is skepticismabout thevalueof suchasystemandhowitwouldaffectthestudyofplantdiversityoverall,itdoesillustratehowbotanistscontinuetothinkaboutnaming,classifying,andinterpretingthehistoryofplantdiversity.

summaRyThroughouthumanhistory,individualshaveworkedtodescribeandorganizethediversityofplantlifeonEarth.Earlyartificialclassificationswerebasedprimarilyuponaplant’susefulnesstohumans.Throughouttime,systematistsdevelopednaturalclas-sificationsthatpresenttheevolutionaryhistoryofplantgroups.Linnaeusisoneofthebest-knownnamesinthehistoryofbotany,butmanydifferentindividualshavecontributedandcontinuetoplayasignificantpartinthisfieldofstudy.

32

Fungiandalgae

Did you hear about the fungus and the alga? They took a lichen to each other.

—Unknown

Although there are many beneficial species of fungi, people often fearthembecauseoftheirtoxinsandotherundesirablefeatures.Forexample,fungicalledmoldscauseallergiesandotherrespi-ratory illnesses. Other species produce strong hallucinogeniccompoundsthathavearangeofeffectsonthenervoussystem.Otherfungi,however,producechemicalsthatbenefithumans.TheimportantantibioticpenicillinisderivedfromthefungusPenicillium chrysogenum. As a further example, the yeast Sac-charomyces cerevisiae isaninvaluablefungususedtomakebread,beer,andwine.

Like so many of the fungi, algae too are often overlookedor unwanted. A thick growth of algae can pollute ponds andrender water undrinkable (Figure 3.1). Fish tanks often needtobecleanedtoremovealgalgrowth.Otheralgae,however,arevaluedfortheirusefulness.NoriandsealettuceareusedinAsiancooking. Carrageenan, a product derived from algae, is usedin ice cream, sauces, shampoos, cosmetics, air fresheners, andmanyotherproducts.Algaearealsoof immeasurableecologi-calimportanceinoceans,lakes,andstreams,wheretheyarethefoundationofthefoodchain.

At different times, fungi and algae have been classified asplants.Althoughthesegroupsdosharesimilaritieswithplants,fungi differ enough to warrant their own kingdom. Whetheralgaeshouldbeplacedinadifferentkingdom,however,dependsonwhichalgaisbeingconsidered.

Fungiandalgaehaveplayedvitalrolesinplantevolution.Anancestralalgalspeciesestablisheditselfintheterrestrialenviron-mentandgaverisetoallplants.Thisinvasionoflandwasmadepossiblethroughinteractionsbetweenplantsandfungi.Becauseearlyplantshadnoroots,plantsandfungiformedrelationshipsinwhichfungiprovidedplantsnutrientsfromthesoil.Amajor-ityofplantstodaystillformtheseimportantsymbioticrelation-shipswithfungi.

34

Fungiandalgae

35Fungi and Algae

FunGIMycology (fromtheGreekwordforfungus,mykes)isthestudyof fungi.Likeplants, fungiaremulticellulareukaryoteswhosecellsproduceacellwall.Fungicellwalls,however,arecomposedpredominantlyofchitin(asubstancealsofoundintheexternalskeletons and shells of insects, crustaceans, and other relatedanimals).

Fungiarecomposedofmanysmallthreadlikestrandsofcellscalledhyphae. The collection of hyphae that make the fungal

Figure 3.1 Excessive growth of algae can reduce the quality of freshwater lakes and ponds.

36 Plant diversity

body is called a mycelium. Fungi range in size from unicellu-lar yeasts to the immensely large individuals that cover greatareasinforests. Fungiareheterotrophsthatfeedonlivinganddeadorganisms.Theyobtainenergyandnutrientsbygrowinghyphae through the body of their food source and secretingenzymesthatbreakitdownintosmaller,simpler,organicmol-ecules,whicharethenabsorbed.Thismethodof feedingmakesfungi,alongwithbacteria,extremelyimportantasdecompos-ersthatclearorganicwastefromtheenvironmentandreturnnutrientstothesoil.

BasIcFunGaLLIFecycLeMany fungi reproduce asexually as well as sexually. In asexual

reproduction,sporesareformedinaspecializedstructurecalledasporangium (plural:sporangia)andthenreleasedtotheenviron-ment.Fungidonothavemaleandfemaleindividuals.Instead,sexualreproductionoccursbetweengeneticallydifferentmating

types.Forsexualreproduction,haploidmyceliaofdifferentmat-ingtypescomeintocontactwithoneanother,allowingcellsfromdifferenthyphaetofuse.Althoughthecellscombine,theirnucleicanremainseparatewithinthemandgrowasamyceliumcom-posedofthesedikaryoticcells.Whethertheseparatenucleifuse

the Humongous FungusWhile several plants are candidates for the title of “largest or oldest organ-ism on Earth,” the fungi kingdom also has individuals of tremendous size and age. The honey mushroom (Armillaria ostoyae) is a fungus that attacks the roots of conifers. The mycelium of one individual in southwest Wash-ington State was measured to cover 1,500 acres (approximately 2.5 square miles). Another, growing in eastern Oregon, covers 2,200 acres (3.4 square miles) and may be more than 2,400 years old.

37Fungi and Algae

immediatelytoformazygoteorcontinuetogrowasadikaryoticmyceliumuntilformingazygoteatalatertimeisadistinguishingfeatureamongdifferenttypesoffungi.

majoRFunGaLGRouPsMycologistshaveidentifiedandnamedmorethan50,000spe-ciesoffungi(Table3.1andFigure3.2)andhaveestimatedthatthetotalnumbermaybecloseto1.5million.Fungiareamono-phyleticgroup,buttheirclassificationhasbeenchallenging.Forexample,recentadvancesinthecollectionandanalysisofgeneticandothermoleculardatahaveallowedmycologiststodeterminethatthewatermolds(Oomycota)andslimemolds(Dictyoste-liomycotaandMyxomycota),whichhadlongbeenclassifiedasfungi,arenotfungiatall,butareinfactprotists.

Presently,mycologistsrecognizefivemajorphyla(equivalenttothebotanicallevelofdivision)offungi:chytrids(Chytrido-mycota), zygomycetes (Zygomycota), arbuscular mycorrhizal

Table3.1 Major Groups of Fungi

Group Common name Estimated species

Chytridomycota chytrids 1,000

Zygomycota zygomycetes 1,100

Glomeromycota arbuscularmycorrhizal 157

fungi

Ascomycota sacfungi 32,00

Basidiomycota clubfungi 26,000

38 Plant diversity

Figure 3.2 Fungi display a wide range of growth forms. In the above pho-tographs; two fly agaric mushrooms (a), cultured Beauveria bassiana (b), a bunch of mushrooms at the base of a withered plum tree (c), and the fungal pathogen Candida albicans, as seen under a microscope (d).

a b

c d

39Fungi and Algae

fungi (Glomeromycota), club fungi (Basidiomycota), and sacfungi (Ascomycota).Currentperspectiveson fungal evolutionindicatethatthechytridsandzygomycetesaretheoldestlineages(Figure3.3).Arbuscularmycorrhizalfungi,clubfungi,andsacfungiaremoreadvancedgroups.Clubfungiandsacfungiarecloselyrelatedandencompass95%ofallknownfungi.

Figure 3.3 This cladogram shows the phylogeny of major fungal groups.

40 Plant diversity

ChytridsChytridomycotaaretheoldestgroupoffungi.Theyliveprimar-ilyinornearwaterandaretheonlygroupoffungitoproducesporesandgameteswithflagella(singularflagellum),atail-likestructure that gives cells the ability to move. The presence offlagellainthislineageprovidesevidencethat,likeallotherorgan-isms,fungifirstevolvedintheseas.

Thechytridlifecycleissimple.Haploidsporesgerminateandformahaploidmycelium,whichreleasesmaleandfemalegam-etes.Thegametesfuseandimmediatelyformadiploidmyceliumthateventuallyformsasporangium.Cellsundergomeiosisinthesporangiumandreleasethehaploidspores.

Chytrids are important decomposers of plant material inmanyaquaticsystems.AchytridcalledBatrachochytrium den-drobatidisiscurrentlyattackingamphibianpopulationsworld-wide and may be responsible for the extinction of severalamphibianspecies.

ZygomycetesZygomycotaarearelativelysmallfungalgroupofabout1,100species.Afrequentlyencounteredzygomyceteisthecommonbread mold in the genus Rhizopus. In asexual reproduction,sporangia form on the tips of upright hyphae and releasenumerousspores.Duringsexualreproduction,fusedhyphaefromdifferentmatingtypesformazygospore(thesmallblackdotsseeninmoldybread).Azygosporeishighlyresilienttoenvironmentalconditionsandcanremaindormantuntilenvi-ronmental conditions cue favorable conditions for releasingspores.

Arbuscular Mycorrhizal FungiMycologists recently moved a group out of Zygomycota andclassified themas anewphylum,Glomeromycota.Their com-monname,arbuscularmycorrhizalfungi,highlightsthisgroup’s

41Fungi and Algae

important features. Mycorrhizae (which literally means“fungalroot”)arefungithatgrowonahostplant’sroots.Theplantpro-vides the funguswithacarbohydrateenergysource. Inreturn,thefungusprovidestheplantwithnutrientsfromthesoil.Thistypeofplant-fungusmutualismoccursinthemajorityofplantsonEarth.Arbuscules arespecializedstructuresformedbythefungusinsidetheplantcellthatenabletheplantandfungustoexchangenutrients.Thearbuscularmycorrhizalfungiaretheonlygroupofmycorrhizalfungithatformthesespecializedstructures.

Arbuscularmycorrhizalfungiareobligatemutualists,mean-ingthattheyareunabletolivewithouttheirplanthost.Mycol-ogists cannot even culture them in the laboratory. Sexualreproduction has never been observed in any member of thisgroup.

Sac FungiAscomycotaisalargegroupthatincludesmorethanhalfofallknownfungi.Theircommonname(sacfungi)comesfromthesac-shaped structure called an ascus (plural: asci) that formsduring sexual reproduction.Asci form on the edge of a largereproductivestructurecalledanascocarp thatischaracteristicofthesefungi.Duringsexualreproduction,differentmatingstrains

chestnut BlightAmerican chestnut (Castanea dentata) once accounted for 25% of the trees in the eastern forests of North America. Then, in the early 1900s, a disease known as chestnut blight was accidentally introduced into North America from China or Japan. The disease, caused by the fungus Cryphonectria para-sitica, attacked native chestnut trees and by 1940 had driven the species to the brink of extinction. In April 2006, however, a small group of chestnuts was discovered near Warm Springs, Georgia. Scientists believe that these trees survived because the site is too dry for the fungus.

42 Plant diversity

fuse,formingadikaryoticmycelium.Themyceliumthenformsanascocarpwiththeascionit.Insidetheasci,thenucleifuse,andthenimmediatelyundergomeiosistoformhaploidspores,whichgerminatetoestablishanewmycelium.

Ascomycetes are important decomposers in many ecosys-tems. The sac fungi also include many species that cause dis-easeinawidevarietyofcropsandwildspecies.Therearealsomanybeneficialascomycetes.ThegenusPenicillium includesthesourceofpenicillin(Penicillium chrysogenum),thebluecheeses(Penicillium roqueforti and Penicillium camembertii), and theyeast used in brewing and baking (Saccharomyces cerevisiae).Morels(Morchella)andtruffles(Tuber)areconsidereddelicaciesbysomeindividuals.

Club FungiThe mushrooms, toadstools, and puffballs common to forestsandfrontyardsaremembersoftheBasidiomycota.Thenameclub fungireferstotheclub-shapedsporangium,calledabasid-

ium (plural:basidia), formedduringsexualreproduction.Asinothergroupsoffungi,thesexualreproductionofbasidiomycetesbeginswiththejoiningofdissimilarmatingstrains.Theresult-ingdikaryoticmyceliumformsareproductivestructurecalledabasidiocarp (thefamiliarmushroom).Thegillsontheunder-surfaceofthebasidiocarpformnumerousbasidia inwhichthedikaryoticnucleifusetoformazygote.Thesingle-celledzygotethenundergoesmeiosistoformhaploidsporesthatarereleasedtogerminateandproducenewmycelia.Thezygoteistheonlydiploidcellintheentirebasidiomycetelifecycle.

Clubfungiareadiversegroupthathasmanydifferentprop-erties and uses. The white button or portabella mushroom(Agaricus bisporus),oystermushroom(Pleurotus ostreatus), andshiitakemushroom(Lentinula edodes) areeatenonsalads,piz-zas,andmanyotherdishes.Amanita bisporigera, Amanita virosa,andAmanita verna areknownasdeathangelfungi becauseof

43Fungi and Algae

theirlethaltoxinsandalmostpurewhitecolor.Flyagaric(Ama-nita muscaria)andpsilocybinmushrooms(Psilocybe cubensis)produce hallucinogenic compounds that have been used byshamans—a religious specialist or medicine man—in ancientcultures and religions worldwide. Shelf fungi are importantdecomposers of wood and other plant materials. Club fungicalled rusts and smuts are serious plant pathogens that causebillionsofdollarsincropdamageannually(Figure3.4).

Figure 3.4 Smut, a fungus that causes plant disease, attacks many cereal crops. Above, mature smut galls are exposed on an ear of corn.

44 Plant diversity

aLGaePhycology, thestudyofalgae,coversawiderangeofphotosyn-thetic organisms—from minute diatoms, whose shells displayintricate patterns and structural variations, to the enormouskelps thatgrow in thecoldoceansofnorthern latitudes.Thisdiversityhasallowedalgaetosucceedinawiderangeofhabi-tats.Algaeliveinsoil,sand,andonthebarksoftrees.Someevengrowinsnow.Manyliveintheoceans,wheretheyformthebaseof marine food webs. Others perform the same ecological rolein freshwaterecosystems.Somegreenalgaehaveevenevolvedunusualassociationswithotherorganisms.

Green algaeareofparticularimportancebecausetheyarethegroupfromwhichlandplantsevolved.Twoothergroups—thered algae (division Rhodophyta)andthebrown algae (familyPha-eophyceae)—arealso includedhere,however,becauseof theirimportanceandfamiliaritytohumans.

Green AlgaeGreenalgaeareancient;theiroriginscanbetracedbackmorethan900millionyears.Throughoutthecourseoftime,theoneoriginalunicellularspeciesdiversifiedtoformotherunicellularspecies, as well as larger, more complex, multicellular growthforms.

GreenalgaLifecycleGreenalgallifecyclesincludesexualandasexualreproduction.Inunicellularalgae,asexual reproductionvia spore formationorcelldivisioniscommon.Sexualreproductioninunicellulargreenalga involves flagellated,haploid individualsofdifferentmating types simply coming together and fusing nuclei. Theresultingdiploidzygospore undergoesmeiosisandreleaseshap-loid unicellular individuals. Cells are also typically haploid inmulticellulargreenalgae.Duringsexual reproduction inmul-ticellular species, some of the haploid cells release flagellated,

45Fungi and Algae

unicellulargametes,which join inaprocess similar to thatofunicellular algae. The resulting single-celled zygote undergoesmeiosisandreleaseshaploidsporesthatgrowtobecomemulti-cellularindividuals.

GreenalgaeLineagesareRelatedtoLandPlantsGreen algae are a large group with more than 17,000 species.Therearethreemajorgroupswithinthegreenalgae:prasino-phytes,chlorophytes,andthecharophytes.Prasinophytesareadiversegroupofunicellularmarinealgae.Thisgroupincludesseveralseparatelineagesand,thus,isnotamonophyleticgroup.Prasinophytesareimportantbecausetheymakeupsomeoftheoldestlineagesofgreenalgaeandarethereforerepresentativeofthefirstgreenalgaetoevolve.

Chlorophytesareagroupofapproximately7,500speciesofgreenalgaethatliveinsaltwater,freshwater,andonland.Theyexhibitanumberofdifferentgrowthformsrangingfromsingle-celled species (Chlamydomonas), filamentous forms (like thegenusOedogonium),spheroidcolonies(suchasVolvox),andthedelicate,sheet-likesealettuces(Ulva).

Charophytes are predominantly freshwater or terrestrialalgae,althoughsomelive inbrackishwater(acombinationof

it's not Easy Being GreenAlgae are well known for their mutualistic relationships with fungi. Less well known, however, are their mutualistic relationships with animals. One such relationship involves the sloth, a mammal that lives in the canopy of tropi-cal forests. The sloth gets its greenish hue from the algae that live in its fur. This coloration helps camouflage the sloth, protecting it from predators. In return, the algae get a place to live and exposure to the light that is present high in the forest canopy, where sloths usually dwell.

46 Plant diversity

saltandfreshwater).Charophytes,likechlorophytes,includeadiversity of unicellular and multicellular growth forms. SomecharophytesintheorderCharales arecalledstonewortsbecauseofcalciumdepositsintheircellwalls,atraitthathashelpedpre-serveevidenceoftheminthefossilrecord.ThegenusSpirogyra contains many filamentous species commonly encountered infreshwaterlakesandponds.

RelationshipBetweenGreenalgaeandPlantsGreenalgaeshareanumberoftraitswithplants,buttheyalsodifferinimportantways.Algaelackasterilejacketlayeraroundtheirgamete-producingstructures.Inaddition,avastmajorityofalgaereleasetheirgametesintothewater,whereasthefemalegameteisretainedonthematernalindividualinplants.

Charophytesare theonlyorganismsother thanplants that producepigmentscalledflavonoids.SpeciesinthegeneraCharaandCholeochaetealsohavereproductivetraits,suchasflagellatedspermandnonmotileeggs,thataresimilartoterrestrialplants.Speciesinthesegroupsalsoretainthezygoteinthegametophytetissues,buttheylackthesterilejacketcellsfoundinplants.Sys-tematistsbelieve thatalgae in theChara lineageare the livingdescendentsofacommonancestorsharedbygreenalgaeandlandplants.Althoughsystematistsagreethatlandplantsevolvedfromagreenalgaancestor,thereiscontinuingdiscussionaboutwhetherplantsandgreenalgaeshouldbegroupedtogetherorseparately.

Red Algae (Rhodophyta) and Brown Algae (Phaeophyceae)Thedebateabouttheexactrelationshipbetweengreenalgaeandmodernplantsdoesnotextendtotheredandbrownalgae.Thesegroups differ from plants in several ways. Because they sharestructural featureswith thegreenalgae,however,andbecausethey are photosynthetic autotrophs, they are included in thisdiscussionofgroupsthatarerelatedtolandplants.

47Fungi and Algae

Brownalgaeareasmallgroupofapproximately1,500spe-ciesthatlivemostlyalongtherockyshoresofcoldoceanwaters.Kelpisanimportantbrownalgathatformsextensiveunderwater“forests.”Thekelpbodyhasthreespecializedregions:aholdfastthatanchorsthekelp,astipe(orstem),andblades(leaves).Bladesoftenhaveafloat,whichisanair-filledstructurethatholdsthekelpupright.Amongotherthings,brownalgaedifferfromplantsinthephotosyntheticpigmentstheycontain.

Redalgaearealargegroupofapproximately6,000marinespecies,mostofwhicharemulticellular.Theygettheircharac-teristiccolorfromthehighamountofreddishpigmentscalledphycobilins intheircells.Thesepigmentsareparticularlygoodatabsorbingwhatlittlelightthereisinthedeepwaterenviron-mentswheremanyredalgae species live.Thedeepestknownphotosyntheticorganismisaredalgathathasbeenfoundliv-ing268metersbelowthewater’ssurface.Often,thecellsofredalgaearecoveredbyajellylikesubstance(mucilage)orcontaindepositsofacertaintypeofmineral(calciumcarbonate);thesematerials help the red algae survive in deep water. Althoughsome red algae produce toxic substances, they do not causetheredtidesthatkillfishandothermarinelife.Redtidesareactuallycausedbypopulationexplosionsofprotistsknownasdinoflagellates.

LIchensLichensareinterestingorganismsthatdevelopfromamutualismbetweenfungiandalgaeorcyanobacteria.Morethan98%ofthefungithatformlichensareascomycetes,butafewbasidiomycetesalsoformlichens.

Inlichens,manyunicellularalgaeliveembeddedinafungus(Figure3.5).Thealgaeprovidecarbohydratesandothernutri-entstothefungus,whichinturnprovidesalivableenvironmentforthealgae.Lichensexistinextremelystressfulenvironments,suchastreebranchesorbarerock,inwhichneitherthefungus

48 Plant diversity

noralgaecouldlivealone.Thisabilitytosurviveinharshenvi-ronmentsallowslichenstobeamongthefirstcolonizersofbarerocksurfaces.

Figure 3.5 Lichens are symbiotic organisms with algae embedded in a fungal matrix. The above image is of Lobaria pulmonaria, the most widespread Lobaria lichen, photographed in Oregon.

49Fungi and Algae

Lichensdisplaythreedifferentgrowthforms.Crustoselichensareflat;theyoftenappeartobepaintedonthesurfaceswheretheygrow.Foliose lichens have a leafy appearance.Fruticose lichensrange in appearance from the multibranched individuals ofreindeermoss(Cladonia subtenuis)totheerectpillarsofBritishsoldier(Cladonia cristatella).Despitetheirabilitytotoleratethehot,dry,brightconditionsofbarerock,lichensarequitesensitivetoairpollution.Environmentalscientiststhereforeuselichensasindicatorsofairpollution.

summaRyAlthoughtheyarenotplants,fungiandalgaeareimportantinanydiscussionofplantdiversityandevolution.Fungiaremul-ticellular, heterotrophic organisms. Their ecological functionasdecomposersmakesnutrientsinthesoilavailabletoplants.Symbiotic relationships with mycorrhizal fungi allowed earlyplants to colonize the land, and continue to help them still.Greenalgaeareadiversegroupofunicellularandmulticellularphotosyntheticorganismswhosecharacteristicsindicatethatallterrestrialplantsevolvedfromasinglealgalancestor.

50

seedlessnonvascularPlantsTheBryophytes

. . . the peat of the valley of the Somme is a formation which,in all likelihood, took thousands of years for its growth.

—Charles Lyell (1797–1875)British geologist

More than 500 million years ago, a multicellular species of alga becamethefirstorganismtomakethetransitionfromlivinginthewatertolivingonland.Livinginshallowwaters,thisances-torofallplantsexperiencedalternatelywetanddryconditionswiththeriseandfallofthetides.Traitsevolvedinthisspeciesthatalloweditnotonlytotoleratethedryperiodsatlowtide,butalsotosurvivefartherfromtheedgeofthewater.Fromthesesimplebeginnings,KingdomPlantaewasborn,andthebotanicalinvasionoflandhadbegun.

Plantsadaptingtolandhadtoovercomecertainchallenges;airdoesnotprovidethestructuralsupportorthenutrientsthatwaterdoes.Inresponsetothesenewenvironmentalconditions,earlyplantsbeganproducingacuticle—athickenedlayerofwaxymaterialontheoutersurfaceofcellsthatpreventedthemfromdryingout.Theplantswereprobably thin, allowingnutrientstoenterandspreadthroughouttheplantbody(vascular tissueforspecializedtransportwouldnotevolveforanother50to100millionyears).

Althoughoftenoverlookedbecauseoftheirdiminutivesize,bryophytes(Figure4.1)arethelivingdescendentsoftheseearli-estplants.Bryophytesarenonvascularplants. Therearebetween20,000 and 25,000 species of bryophytes (Table 4.1) classifiedinto three divisions: liverworts (Hepatophyta), hornworts(Anthocerotophyta)andtruemosses(Bryophyta).Thesemod-ernbryophyteshaveretainedmanyfeaturesoftheirancestors;forexample,theyproducenovasculartissueorseeds.Becauseofthis, thestudyofbryophytescanprovideinsightintosomeofthefirststrategiesevolvedbyplantsintheiradaptationtolifeonland.

FeaTuResoFBRyoPhyTesBryophytesaretypicallysmallplants,rangingfromafewmillime-terstoseveralcentimetersinheight.Theirsizeislimitedbecausetheylackvasculartissue,whichprovidesthestructuralsupportand nutrient transport necessary for larger growth. Instead of

52

seedlessnonvascularPlantsTheBryophytes

53

Figure 4.1 Bryophytes are small, nonvascular plants. Above, green moss (a type of bryophyte) covers three oak tree trunks.

Seedless nonvascular Plants

54 Plant diversity

usingrootstotakeupwaterandanchorthemselvesinplace(asplantsdo),bryophytesusespecializedcellscalledrhizoids.Unlikerootcells,rhizoidsdonothaveanygreaterwateruptakeabilitythantherestoftheplant.Mostbryophytesusetheirentirebodiestogatherwaterandnutrientsfromtheenvironment.

Althoughsomebryophytescansurviveinverydryhabitats,avastmajorityofbryophytesliveinmoistenvironments(Figure4.2). Bryophytes are restricted to moist environments partlybecausetheylackvasculartissue,butalsobecausewaterisrequiredforspermtoswimtotheeggsduringsexualreproduction.

BRyoPhyTeLIFecycLeThelifecycleofbryophyteshasdistinctgametophyteandsporo-phytegenerations.Thefree-livinggametophyteisthedominantphase. The short-lived sporophyte is attached to and nutri-tionally dependent upon the gametophyte. The structure andappearance of gametophytes and sporophytes differ amongbryophytegroups.

Haploid spores germinate into small, threadlike, multicel-lulargametophytescalledprotonemas.Theseprotonemasmatureand produce gametophytes with antheridia (sperm-producingstructures),archegonia (egg-producingstructures),orboth.Mostbryophytes produce antheridia and archegonia on the same

Table4.1 Major Groups of Bryophytes


Anthocerotophyta hornworts 100–150

Hepatophyta liverworts 6,000–9,000

Bryophyta truemosses 12,000–15,000

55Seedless nonvascular Plants

Figure 4.2 Mosses are common in moist, streamside habitats. In this photograph, moss is present on a boulder near Silverton, Colorado.

56 Plant diversity

gametophyte,butmossesproduceantheridiaandarchegoniaonseparatemaleandfemalegametophytes.

Becausethespermmustswimtotheegg,maleandfemalegametophytes must grow near one another. Sperm cells usewhiplike flagella topropel themdownanarrowcanal towardtheegg.Afterfertilization,thecombinedeggandspermformadiploidembryothatwillbecomethesporophyte.Theyoungspo-rophyteisattachedtothegametophyteandwillremainattachedtothegametophyteforitsentirelife.Asporangiumformsatthetipofthesporophyte.Sporemothercellsinsidethesporangiumwillundergomeiosistoformthehaploidsporesthatwillstartthecycleoveragain.

majoRGRouPsoFBRyoPhyTesBryophytes are a relatively small group of plants containingapproximately 24,000 species. All bryophytes are structurallysimple plants, and the major groups differ primarily in theirreproductivestructures.

Figure 4.3 Marchantia is a typical liverwort. It is a primitive plant related to mosses and ferns.


LiverwortsLiverwortsarethesecondlargestbryophytedivision,with6,000–9,000species.Thebasicbodyformofaliverwortconsistsofasimple,flattened,leaflikethallus,thathasaverysimplebranchingpattern(Figure4.3).Theseplantsareinacladecalledtheleafyorsimplethallusliverworts.Theremainderoftheliverwortsareinacladecalledthecomplexthallusliverworts.Theseplantshaveabroader,flattenedthalluswithpronouncedstructuraldiffer-encesbetweentheirupperandlowerlayers.

Thegenus Marchantiacontainsspeciescommontocool,shady,moistareasnearstreamsandwaterfalls.Marchantia producessep-aratemaleandfemalegametophytes.Themalesproduceanther-idiaonraisedflattenedstructureswhich,whenhitwithadropofwater,launchthespermfromthegametophye.Femalesproducearchegoniaonaraisedstructurethathasadroopingappearance.The sporophyte is a small, rounded structure attached to theundersideofthefemalegametophyte.Gemmae (singular:gemma)aresmallmassesoftissuethatmayformincuplikestructuresonthethallus.Thesemassesofvegetativecellscansplashoutofthecups, allowing theparentplant to reproduceasexually throughvegetative reproduction.Marchantiamayalsoreproducevegetativelybyfragmentationofpartsfromalarger,olderplantbody.

doctrine of SignaturesLiverworts and an assortment of other plants include the names of various organs in their common names. This comes from a belief known as the Doctrine of Signatures. Early physicians and herbalists thought a plant that resembled an organ could be used to treat ailments of that organ. The lobed liverwort thallus was used to treat liver complaints because it resembles a human liver. The suffix -wort comes from the Old English word wyrt, meaning “herb.” The Doctrine of Signatures was a popular medical concept through the nineteenth century and is still used by some practitioners of homeopathic medicine.

58 Plant diversity

HornwortsHornwortsarethesmallestbryophytedivision,with12generaandonly100–150species.Liketheliverworts,theyproduceantheridiaandarchegoniaontheuppersurfaceofathallus.Inhornworts,however, the sporophyte grows from the upper surface of thethallusandhasanelongatedhornorspindleshape(Figure4.4).Hornworts resemblevascularplants in that their sporophyte isphotosyntheticandproducesstomata(openingsthatallowwaterandgassestobeexchangedbetweentheplantandtheatmosphere).Theproductionofstomatamaybeanimportantevolutionarylinkbetweenhornwortsandplantsthatevolvedlater.

MossesThemostfamiliarofthebryophytes,mosses,areaverysuccessfulgroup,with12,000–15,000species.Theygrowinawiderangeofconditionsrangingfrommoistareasalongstreamsandinforeststoarcticandalpineenvironments.Mossesaretypicallydividedinto

Figure 4.4 Hornworts are most commonly found in damp, humid, undisturbed locations. Hornworts are seen here in Lincoln County, Oregon.


threeclasses:peatmosses(Sphagnopsida),granitemosses(Andre-aeopsida), and true mosses (Bryopsida). The peat mosses are asmallgroupwithtwogeneraandmorethan400species.Sphagnum peatbogs coverapproximately1%oftheEarth’ssurface.Granitemosses areaneven smallergroupof approximately100 species.These blackish-green or reddish-brown mosses grow in clumpsinmountainsandgraniteoutcrops.Thetruemossesarethemostcommon.Althoughindividualplantsaresmall,mossgametophytescandominatethelandscapewithextensivematsofvegetation.

Themosssporophytegrowsfromthetopofthefemalegame-tophyte.Thematuresporophyteiscomposedofacapsuleonthetipofalongstalkcalledaseta.Whenmature,thecapsuledries,releasingthenumeroussporesinside.

Similartovascularplants,mossesproducespecializedtrans-portcells.Cellscalledhydroidsarefoundinthecentralstemofsomemossspecies,andfunctiontotransportwaterupthemossstem.Cellscalledleptoidstransportsugars.Althoughtheyfunc-tionlikevasculartissue,hydroidsandleptoidslacksomeofthedefining features of true vascular tissue. Many mosses have aleafyappearancewithareasofphotosynthetictissuethatresem-bleleaves.Becausethesestructureslackvasculartissue,however,theyarenot true leaves.Nevertheless, suchfeatures indicateacloserelationshipbetweenmossesandvascularplants.

A Moss By Any other nameConfusion between common and scientific names is nowhere more evident than in the term moss. Technically, mosses are the plants in the group Bryophyta. The name moss, however, is applied to various plants and nonplants outside of this group. Irish moss and the moss in ponds and lakes are actually algae. Spanish moss and rose moss are angiosperms. Club moss and spike moss are seedless vascular plants related to ferns. Reindeer moss is not a plant at all, but rather a lichen.

60 Plant diversity

oRIGIns,DIVeRsIFIcaTIon,anDPhyLoGenyoFTheBRyoPhyTesSporesandfragmentsofancientbryophyteshavebeenfound infossilsthatdatebackalmost445millionyears(Table4.2).Thesefos-silsandotherdatasuggestthatbryophytesevolvedfromtheiralgalancestorbetween490and500millionyearsago.Bryophytesprob-ablydivergedfromthelineagethatgaverisetovascularplantsabout430millionyearsago.Fossilsofancientliverwortshavebeenfound

Table4.2 The Geological Timescale

Eras Periods Beginning (mya)* Major botanical events

Quarternary 1.8

Cenozoic Tertiary 65 Radiationoffloweringplants

Cretaceous 144 Evolutionoffloweringplants

Mesozoic Jurassic 206

Triassic 248 Conifersdominant

Permian 290

Carboniferous 354 Forestsoflarge,primitivetrees

Paleozoic Devonian 417 Seedlessvascularplants

dominate,firstseedplants

Silurian 443 Firstvascularplants

Ordovician 490 Plantsinvadeland

Cambrian 543

Precambrian 4550 FormationofEarth

*mya:millionyearsago


inrocksdatingback360to408millionyears,andmossfossilshavebeenidentifiedfromasfarbackas290to360millionyearsago.

Untilrecently,allbryophyteswerethoughttohavedescendedfromasingle,commonancestor.Newevidenceindicates,how-ever, that bryophytes are actually three distinct monophyleticlineages.Thearrangementofthethreelineages,however,isnotcompletely certain. Traditionally, systematists believed horn-wortstobeoldest,withliverwortsthenextoldest,andmossesthemost recentlyevolvedgroupofbryophytes.Somestudies,however, have suggested that hornworts may actually be themostcloselyrelatedtovascularplants.

ecoLoGIcaLanDeconomIcImPoRTanceEcologically, bryophytes are important plants. They grow inextensive mats and colonies that can help stabilize soils nearstreams.Theymaycolonizedisturbedsitesearly,beginningtheprocessofecologicalsuccession inwhichtheplantsgrowingonasitechangesovertime.Mossesareimportantcomponentsoffoodchainsinmanyarcticandalpineenvironments.

Economically, bryophytes are of some importance. Sphag-num mosshasavarietyofdifferentuses.Inthepast,it wasusedtodressandpackwounds.Peat,whichislargelySphagnum, isburnedasfuelinsomenortherntemperateareas,inhomesandinlarger-scaleelectricityproduction.Peatisalsoimportantinthehorticultureindustrywhereitisusedtolightenandincreasethewater-holdingcapacityofsoil.

summaRyLiverworts, hornworts, and mosses are nonvascular, nonseed-producingplants.Knowncollectivelyasbryophytes,thesewerethe firstplants tosuccessfully invade,establish,andpersistonland. True to their aquatic origins, however, they still dependonwatertotransportspermtoeggduringsexualreproduction.Bryophytes are the only plants with a dominant gametophytestageandasmallersporophytestage.

62

seedlessVascularPlants

Nature does not proceed by leaps and bounds. —Carolus Linnaeus

The coal that powered the Industrial Revolution in the eighteenthandnineteenthcenturiesisstillanimportantfuelsourcetoday.Coalformationbeganmorethan300millionyearsago,whenshal-lowseascoveredtheEarthandawarmtropicalclimatepromotedlushplantgrowth.Treesandplantsthatfellintothewaterastheydieddidnotdecomposebecausethelowoxygencontentofthewaterpreventedit.Overtime, layersofsedimentsaccumulatedontopoftheplants,whichforcedthewateroutoftheirtissues.Duringthecourseofmillionsofyears,theintensepressureandheatofgeologicforcesconvertedtheplantsintocoal.

Onegenusof tree, inparticular, contributedagreatdealofplantmattertothecoalbeds.ThetrunksofLepidodendron treesstoodmore than130 feet (40meters) tall andweremore than6 feet (2 meters) in diameter. They and their relatives formedextensive forests. Lepidodendron and many of the other plantsthateventuallybecamecoalweremembersofagroupcalledtheseedlessvascularplants.Unlikethebryophytesbeforethem,theseplantsevolvedvasculartissue,anetworkofxylemandphloemthattransports water, nutrients, and other materials efficiently andeffectivelyaroundtheplantbody.Thisandotherimportanttraitsmadethenextgreatbreakthroughinplantevolutionpossible.

Many different lineages of seedless vascular plants havebecome extinct since they first evolved. At present, seedlessvascularplantsconsistofapproximately14,000species intwomonophyletic clades (Table 5.1). The oldest clade, the lyco-phytes (division Lycopodiophyta), contains three orders: theclubmosses(Lycopodiales), spikemosses(Selaginellales),andquillworts (Isoetales). The second clade, previously known asthefernsandfernallies,isthemonilophytes. Thisclade containshorsetails(Equisetales),whiskferns(Psilotales),ophioglossoidferns (Ophioglossales), marattioid ferns (Marattiales), waterferns(SalvinialesandMarsileales),andthetrueferns(Filicales).Themonilophytessharedacommonancestorwiththelineagethateventuallygaverisetoseedplants.

64

seedlessVascularPlants

65Seedless Vascular Plants

FeaTuResoFseeDLessVascuLaRPLanTsSeedlessvascularplantswerethefirsttoevolvevasculartissue.These plants, along with the gymnosperms and angiosperms,formagroupcalledthetracheophytesorvascularplants.Themostprimitivetypeofwater-conductingcells,tracheids, arefoundinthexylemofseedlessvascularplants.Thesecellsarerigidduetothepresenceofligninintheircellwalls.Networksoftracheidsnotonlyaidthepassageofwater,butalsosupporttheplantbody.This internal reinforcement of the stem allowed plants of theCarboniferoustoreachgreaterheightsthaneverbefore.Eventu-

Table5.1 Major Groups of Seedless Vascular Plants


Lycopodiales clubmosses 380–400

Selaginellales spikemosses 700–750

Isoetales quillworts 125

Psilotales whiskferns 15–17

Equisitales horsetails 15–25

Ohioglossales ophioglossoidferns 75–110

Marattiales marattoidferns 200–240

Marsiliales waterclover 75

Salviniales waterspangles, 16

mosquitoferns

Filicales trueferns 11,500–12,000

66 Plant diversity

ally,plantsevolvedthemechanismstoproduceandaccumulatexyleminthestem,whichledtotheevolutionofwoodandevenstrongerstemsandbranches.

Withvascular tissue,cametheevolutionof leaves.Leavesarethin,flattenedareasofphotosynthetictissuesurroundinganetworkofveins.Leavesevolvedfromhighlybranchedstemsof early vascular plants, when photosynthetic tissue filled inthespacesbetweenthefinestbranchesatthetipsofthestems.Vascularplant leavesandstemshavea thickcuticle layerontheiroutersurfacethatpreventswaterloss.Leavesalsobecamemuchmoreelaborateandstructurallydiverseinseedlessvas-cularplants.Thefernsinparticularevolvedlargeleavescalledfrondsthatproducesporangiaontheirundersideinmanyspe-cies(Figure5.1).

Plants were evolving new structures below ground as well.Instead of the simple rhizoids that attach bryophytes to theground, the first vascular plants evolved roots. Larger rootsenabledplantstoextractwaterandnutrientsfromthesoilmoreeffectively. Larger roots also provided a stronger anchor andbetterstructuralsupporttothelargerstemsthatwereevolvingaboveground.

Thelifecycleofseedlessvascularplantsalsodivergedfromthat of their bryophyte ancestors. While the sporophyte inbryophytesissmallandcompletelydependantuponthegame-tophyte, the gametophyte and the sporophyte in the seedlessvascularplantscanbeafree-livingplant.Furthermore,unlikethebrypophytes,thesporophytedominatesthelifecycleinseed-lessvascularplants.

Thesechangesinthevasculartissue,leaves,andsporophytepromotedthesuccessof theseedlessvascularplants.Vasculartissueandleaveshelpedplantssurviveinaterrestrialenviron-ment and allowed them to colonize drier areas on land. Thedominant sporophyte also allowed the plants to produce farmoreoffspringthanbryophytes.


seeDLessVascuLaRPLanTLIFecycLeThe life cycle of a typical fern serves as a good example ofthe alternation of generations in seedless vascular plants.Spores are released from sporangia on the undersurface ofthe leaves. The spores germinate to form an independent,heart-shaped,photosyntheticgametophyte.Atmaturity, theantheridiareleasethesperm,whichswimtoandfertilizetheegghousedinthearchegonium.Afterfertilization,theembry-onic sporophyte grows from the gametophyte, which thenwithersanddieswhilethesporophytebecomestheplantweknowasafern.

Anothersignificantchangeinvolvingthesporesoccurredintheseedlessvascularplants.Inthebryophytesandearliestvas-cularplants,allsporesproducedbyaplantareidentical(homo-

spory),producinggametophyteswithantheridiaandarchegonia(mosseshaveseparatemaleandfemalegametophytes,butthey

Figure 5.1 Sporangia are found on the underside of fern fronds. Spo-rangia contain spores, and when the walls of the sporangium dry out, the spores catapult away from the plant.

68 Plant diversity

comefromidenticalspores).Somevascularplantsevolvedtheability to produce different spores (heterospory). Microspores,producedinamicrosporangium, giveriseto malegametophytes.Megaspores, produced in a megasporangium, make the femalegametophyte.Heterosporyisavaluabletraitbecauseitallowssomegametophytestobecomespecializedforspermproduc-tionandothersforeggproduction.Thiswasanimportantsteptowardtheevolutionofpollenandseedsthatwouldoccurlaterinthegymnosperms.

majoRGRouPsoFseeDLessVascuLaRPLanTsSeedless vascular plants include a diverse array of more than25,000 species. Members of the major groups display a widerangeofgrowthforms,lifecycles,andotheradaptationstotheenvironmentswheretheylive.

LycophytesLycophytesarearelativelysmallgroupofplantswith3families,10to15genera,andapproximately1,200species.Alllycophyteshave simple leaves (microphylls) that contain a single strandof vascular tissue. Lycophytes include the club mosses, spikemosses,andquillworts.

Club MossesClubmosses(Lycopodiales)areasmallgroupwith3generaandapproximately380to400species.Thesporophyteisalow-growingterrestrialplantwithsimplebranchingstems(Figure5.2). The plant spreads by a rhizome and has rudimentaryroots.Thesmall,scalelikeleavesbeararesemblancetothoseof many conifers, hence the common name “ground pine”giventosomeclubmosses.Leavesareoppositeoneanotheronthestem.

Sporesareproducedinsporangiaonspecializedleavescalledsporophylls, whichareoftenclusteredattheendsofbranches


into a structure called a strobilus or cone. Club moss game-tophytes are either photosynthetic or obtain nutrition fromorganic material in the soil through symbiosis with mycor-rhizalfungi.

Spike MossesTheorderSelaginellaleshasonly1genus(Selaginella) and700–750species.Thesporophyteisabranchingrhizomesimilartothat of club mosses; whereas the leaves of club mosses growoppositeoneanother,spikemossesproduceleavesinfourrows:tworowsofsmallleavesabovetworowsoflargerleaves.Theseleaveshaveascalelikestructureontheirbase.

Althoughmostspikemossesliveinthetropics,someliveindryenvironments.Theseso-calledresurrectionplantsbecomedormantwhenwaterisscarce,takingonalifelessappearance,onlytospringbacktolifewhenrehydrated.

Figure 5.2 Lycopodium is a typical club moss. Above, stiff club-moss (Lycopodium annotinum) is found in the Pocono Mountains, in Pennsylvania. Note the brown strobili at the ends of the branches.

70 Plant diversity

Quillworts Isoetalesisthesmallestlycophyteorder,withonlyasinglegenus(Isoetes)and125species.Quillwortsarerelativelysmallaquaticplantsthatliveunderwaterforpartoralloftheirlife.Thespo-rophyteisaperennialcormthatcanbesomewhatwoody.Tuftsoflong,quill-likeleaves,mostofwhicharecapableofproducingsporangia,growfromthetopofthecorm.

MonilophytesMonilophytesarea largediversecladecontainingmorethan12,000 species. All monilophytes produce megaphylls, leavesthat have multiple strands of vascular tissue. There are sixmajorgroupswithinthemonilophytes:horsetails,whiskferns,ophioglossoid ferns, marattioid ferns, water ferns, and trueferns.

Whisk FernsWhiskfernsareabsentfromthefossilrecord.Psilotalesisaverysmallorder,withonly2generaand15–17species.ThegenusPsilotumgrowsintropicalandsubtropicalareas.Psilotumhasasimplebodywithsmall,scalelikeleavesandastemthatbranchesoffintotwosmallerstems.Plantshavenoroots;theyspreadbyan underground rhizome covered with rhizoids. Both sporo-

diminutive descendents of GiantsCompared to other species of seedless vascular plants, quillworts are quite small, often being mistaken for clumps of grass—something that would never have happened to their lycophyte ancestors. Recent analyses have shown that the small quillworts of today are the living descendents of the giant lycophyte trees that once dominated swamp forests more than 350 million years ago. Why only small plants from the different seedless vascular plant lineages survived to the present is a mystery that botanists are still trying to solve.


phytesandgametophytesformrelationshipswithmycorrhiozalfungi.Psilotum hasdistinctivesporangiathatareborneinclustersofthreeonthestem.

HorsetailsEquisetaleswasonceadiversegroup,butitnowcontainsonlyasinglegenus(Equisetum)with15–25species.Thehorsetailsareperennialsthatgrowinmoistareasandalongwaterways.Although modern horsetails may reach heights of about 1meter, ancient horsetails known as calamites grew to treesize.

Horsetails have a unique appearance. Branching rhizomessend up aerial stems, whose silica deposits give them a roughtexture.Theridgedstemisessentiallyahollowtubeofseparatesegments.Atthejointsofthesegmentsthereareringsofsmall,scalyleaves.Ovalsporangiaatthetipsofthestemsproducethespores.

Ophioglossoid FernsOphioglossales, also called adder’s tongue ferns, are a smallgroupwith80–90species.Theleavesofthesefernsaredividedintotwodistinctregions:onethatisphotosyntheticandsterile,and another that is nonphotosynthetic and produces spores.YoungleavesofOphioglossoidfernsarenotcoiledasinothergroups.Theyalsoproduceuprightstems,whichdifferfromthehorizontalstemsoftrueferns.Thesporangiaofophioglossoidfernsdevelopfromagroupofcells,unlikethesporangiaoftruefernsthatdevelopfromasinglecell.

Marattoid FernsMarattialesisalsoasmallgroup,withonly6generaandabout200species.Marattoid ferns, likeOphioglossoids,produceuprightstems.Their leavesare large, andwhenyoung,arecoiled into

72 Plant diversity

astructurecalledafiddleheadorcrozier that uncoilsasitopens(Figure5.3).Thesefernsalsoproduceasporangiumthatdevel-opsfrommultiplecells.Thesefernswerecommoninswampsandarewellrepresentedinthefossilrecord.

Figure 5.3 The fiddlehead is an identifying feature of marattoid and true ferns. Above, a fiddlehead is seen unraveling.


Water FernsWaterfernsgrowinfreshwaterpondsandlakes.Therearetwodifferentordersofwaterferns,MarsilealesandSalviniales.Bothare small groups, with approximately 75 species in Marsilealesandonly16speciesinSalviniales.Marsileaplantsgrowinshallowwaterormudandproducefrondswithlongpetiolesandleavesthatlooklikeafour-leafclover.FernsinSalvinialesproducetwotypesoffronds;oneisflattenedandfloatsonwater,andtheotherisfeatheryandhangsbelowthesurfaceofthewater.Thefloatingfrondscontaincoloniesofcyanobacteriathatfixnitrogenforthefernand,consequently,increasethenitrogeninthewaterwheretheygrow.Despitethis,waterfernscanbepestsinsomeareas.Bothgroupsofwaterfernsencasetheirsporesinahardstructurethatcanliedormantinthemudformanyyears.

True FernsFilicalesisthelargest,mostcommongroupofseedlessvascularplants.Therearemorethan11,000speciesin320generadividedamong 30–35 families. As mentioned previously, true fernshaveseveralfeaturesthatseparatethemfromotherferngroups.Theirstemstypicallygrowhorizontallyasrhizomes,andtheiryoungfrondsformfiddleheads.Truefernsarehomosporous.Theirsporangiadevelopfromsinglecellsontheundersurface

noxious Weedy FernsMany ferns are attractive and desired plants. Others, however, are not. Two water ferns, Salvinia molesta (kariba-weed) and Azolla pinnata (feathered mosquito fern) are aggressive, noxious weeds that can clog waterways and cause flooding. Bracken fern (Pteridium) can invade pastures and choke out native pasture plants. This is particularly problematic because bracken fern fronds contain chemicals that are toxic to cattle that eat them.

74 Plant diversity

of fronds. Sporangia are clustered into structures called sori

(singular:sorus)thatareoftencoveredbyaflapoftissuecalledan indusium. Each sporangium has a thickened layer of cellscalledanannulusalongonesideofthesporangium(Figure5.4).Tensiongeneratedbytheannuluscausesthematuresporan-giumtoopenandflingsporesawayfromtheparentplant.

Truefernsgrowinmanytemperateecosystems,buttheyareparticularlycommonintropicalareas.Fernsdisplayadiversityofgrowthforms,includingvines,smallherbs,andevenaquaticherbs. Large tree ferns grow in many tropical forests (Figure5.5).Smallerfernsarecommoninthemiddlelayers(knownas

Figure 5.4 The annulus is a thickened area on the fern sporangium. Above, spores are released from the sporangium.


Figure 5.5 Tree ferns are the largest living, seedless vascular plants. The above image shows tree ferns in Malaysia.

76 Plant diversity

theunderstory) offorestsworldwide.Somefernspeciesdonotproduceasporophytestageatallandexistonlyasgametophytes.Thus,thesespeciesonlyreproduceasexually.

oRIGInsanDReLaTIonshIPsoFseeDLessVascuLaRPLanTsTheoldestvascularplantfossilsareofCooksoniaanddatebackapproximately410millionyears(Table4.2).Theseweresmall,simple,leaflessplantsthatspreadbybranchingrhizomes.Theyspreadbyacentral stemthatgrewalongthegroundandpro-duceduprightbrancheswithsporangiaattheirtips.Theylackedroots,andappeartohaveusedsymbioticrelationshipsbetweentheirrhizoidsandfungitoimprovenutrientuptakefromthesoil.Woody growth evolved approximately 380 million years ago.Productionofwoodevolvedindependentlyinseveraldifferentlineages.

The early vascular plant lineages Rhinophyta, Zosterophyl-lophyta,andTrimerophytadominatedthelandscape425to370millionyearsago,butallthreelineageswereextinctbyabout360millionyearsago.Duringthistime,manyspeciesbecameextinctduetothedryingoftheenvironmentthatoccurredduringthattime.Onlytheferns,herbaceous lycophytes,andhorsetail lin-eagessurvived.

Seedless vascular plants can be divided into two distinctmonophyletic clades (lycophytes and monilophytes) that arewellsupportedbyfossil,genetic,andstructuraldata.Thesplitbetweenthelycophytecladeandothervascularplantsprobablyoccurredmorethan400millionyearsago.Thesplitbetweenthemonilophytecladeandtheseedplantsoccurred20–30millionyearslater.

VaLueoFseeDLessVascuLaRPLanTsSeedlessvascularplantsarecomponentsofmanyterrestrialeco-systems.Livingseedlessvascularplantsareoflimitedeconomicvaluebeyondtheirusefulnessinlandscapingandashouseplants.


Fiddleheadsfromsomespeciesareedible,andclubmosssporeswereonceusedasanexplosiveinfireworksandinthedevelop-ment of photography. Long-dead seedless vascular plants thatbecamecoal,however,areofimmensevalueasaneffectivefuelsource.

summaRySeedless vascular plants evolved more than 400 million yearsago.Theevolutionofvasculartissueenabledplantstobecomelargerbecauseofincreasedstructuralsupportandmoreefficienttransportofmaterialsaroundtheplantbody.Initiallyquitesmall,seedless vascular plants diversified and evolved many massivespecies thatwereonce thegiantsof theancientswamps.Pres-ently,therearetwomajorlineagesofseedlessvascularplants,thelycophytesandthemonilophytes.

78

nonfloweringseedPlantsTheGymnosperms

The pine tree lives a thousand years.The morning glory flower lives a single day.

Yet both fulfill their destiny. —Chinese proverb

The Namib Desert, one of the driest places on Earth, is home to oneofthestrangestplantsonEarth.Welwitschia mirabilissurvivesbyproducinglongtaprootscapableofaccessingwaterfromdeepinthesoil(Figure6.1).Theplantsalsocollectwaterfromcoolfogsthatblowinfromtheocean.Dropletsofwaterthatcondenseontheplant’sleavesflowdownthemtowaterthesoilaroundtheplant.

Unlike other members of the plant kingdom, Welwitschia producesonlytwoleavesduringitsentirelifetime,whichmaylastas longas2,000years.Theleavesemergefromthegermi-nating seed as the plant grows. Harsh desert winds shred theleaves,whichcontinuetogrowfromtheirbase.Theleavesandreproductivestructuresknownasstrobili,orcones, growfromtheedgeofthewoody,bowl-shapedstem.

Welwitschia belongs toagroupofplantscalled thegymno-sperms. The name gymnosperm comes from the Greek wordsgymnos(naked)andsperma(seed). Theseseedsareconsidered

80

nonfloweringseedPlantsTheGymnosperms

Figure 6.1 The desert plant, Welwitschia mirabilis, is photographed in the Namib Desert in Namibia. An adult Welwitschia consists of two leaves, which are torn into strips when the leaves are whipped by strong winds.

81nonflowering Seed Plants

to be naked because they are not covered by sporophyte fruittissues,asangiospermseedsare.ScottishbotanistRobertBrown(1773–1858) was the first to classify gymnosperms as a groupseparatefromtheotherseedplants,basedonthesenakedseeds.

Figure 6.2 Conifers are cone-bearing seed plants that display a vari-ety of shapes and sizes. Above, conifers surround a lake in northern Wisconsin.

82 Plant diversity

Thereareapproximately840 speciesofgymnosperms rep-resentedby4divisions,theconifers(Coniferophyta;seeFigure6.2),cycads(Cycadophyta),ginkgos(Ginkgophyta),andgneto-phytes(Gnetophyta).Somearerestrictedtowarmtropicalareaswhileothersformextensiveforestsincolder,higherlatitudesandareasofhighelevation.Somegymnospermsaregrowncommer-ciallyfordifferentuses.

FeaTuResoFGymnosPeRmsSeedsandpollenaretwofeaturesthathaveenhancedtherepro-ductivesuccessofgymnosperms,allowingthemtoevolveanddiversify. Seeds are an important evolutionary innovationbecause they protect the dormant plant embryos until envi-ronmental signals cue germination. Seeds also contain storedcarbohydrates and nutrients that will feed the seedling as itbeginstogrow.

Pollenisanothercriticaltraittoevolveinthisgroup.Gym-nospermswere the firstplants toproducepollenasaway tocarryspermtotheeggforfertilization.Unlikebryophytesandseedlessvascularplantsthatreleasetheirspermintotheenvi-ronment,thespermcellsofgymnospermsareencasedinpollengrainsthataretransported,typicallybywind,toegg-contain-ingovulesonfemalecones.Whenthepollengraingerminates,apollen tubegrowsintotheovule,andthespermisreleasedtofertilizetheegg.

Seedsandpollenareproducedincones(Figure6.3).Similarto the strobili in the seedless vascular plants, a gymnospermconeisagroupofsporophyllsattachedtoashortcentralaxis.Althoughsporophyllsinmostgymnospermsevolvedasamodi-ficationofaleaf,thefemaleconifercone(pinecone)isactuallynotamodifiedleaf,butratheramodifiedstemaxiscalledacone

scale.Gymnosperms are vascular plants that produce xylem and

phloem.Thegymnospermstemandrootshaveameristemcalled


Figure 6.3 An assortment of female pine cones are displayed above, including a pine cone with open scales (a), a spruce pine cone (b), an eastern white pine cone (c), and a previous year seed cone beside clusters of male cones ( d ).

a b

c d

84 Plant diversity

thevascular cambium,whichproduceswood-formingxylemandbark-forming phloem. All gymnosperms are woody perennialplants.Amajorityofthemgrowastreesorshrubs,andmanyofthemachieveawe-inspiringsizeandage.Avastmajorityofgymno-spermsareevergreen,retaininglivingleavesontheplantthrough-outtheyear.Afew,however,suchaslarch(Larix)andbaldcypress(Taxodium)aredeciduous,sheddingtheirleavesonceayear.

GymnosPeRmLIFecycLeThegymnospermlifecyclediffersfromthoseofbryophytesandferns in its dramatic reduction of the gametophyte stage andincreaseinthesporophytestage.Thesporophyteisclearlythedominant phase. At no point in the gymnosperm life cycle isthereafree-living,independentgametophyte.

Thelifecycleofpines(Pinus) servesasagoodexampleofatypicalgymnospermlifecycle.Thematurepinetreeistheadultsporophyte.Femaleconesareproducedontheendsofbranches.Each female cone is composed of numerous cone scales withfemalesporangiaonthem. Ineachfemalesporangium,aspore

Gymnosperms of unusual Size and AgeSome of the oldest and largest organisms on Earth are gymnosperms. Several bristlecone pines (Pinus longaeva) in the White Mountains of eastern California are more than 4,700 years old. These plants, whose seeds germinated before the pyramids of Ancient Egypt were built, are the oldest known living organ-isms. A coast redwood (Sequoia sempervirens) in the Sierra Nevada Mountains of coastal California is the tallest tree on Earth, standing more than 365 feet (112 meters) tall and calculated to be more than 3,200 years old. The giant sequoia, (Sequoiadendron giganteum), which also grows in California, is another tall gymnosperm species. The tallest sequoias are more than 276 feet (84 meters) tall and 3,500 years old.


mother cell undergoes meiosis to form four spores, but onlyone survives. The single surviving spore undergoes numerousdivisionsbymitosistoformamulticellularfemalegametophytesurroundedbyathinlayeroftissuecalledthe integuments. Thesmallopeningintheintegumentiscalledthemicropyle. Thefemalegametophyteandintegumentsformastructurecalledthe ovule.Insidetheovulearemultiplearchegonia,eachcontaininganegg.

Inthesmall,paperymalecones(Figure6.3d),sporemothercellsundergomitosistoformspores.Eachsporedevelopsintoapollengrainthatcontainsatube cellandagenerative cell.Pineandothergymnospermpollengrainsoftenformairsacs thathelpcarrythemonthewindtothefemalecones.Pollination occurswhenthepollengrainiseitherblowndirectlyintothemicropyleortrappedonadropletofwatersecretedfromthemicropyleanddrawnintoit.Thepollengrainmakescontactwiththefemalegametophyte,germinates,andslowlygrowsapollentubeintothe female gametophyte tissue. When the pollen tube reachesthearchegonium(aprocessthatcantakeuptoayear),itreleasesthespermcelltofertilizetheegg.Theembryoproducedinthefemale gametophyte tissue begins to form a seed. As the seeddevelops during the course of another year, the female conematures,formingthefamiliarwoodypinecone.Oncetheseedsaremature,theconescalesopentoreleasethem,andthecyclebeginsagainwhentheseedgerminatestoformanewseedling.

majoRGymnosPeRmGRouPsGymnospermsarearelativelysmallgroupwithapproximately800livingspecies(Table6.1).Althoughtherearefewspecies,theyarequitecommonandoftenmaintainverylargepopulations.

ConifersWithapproximately60generaandmorethan600species,Conif-erophyta is the largest,mostwell-knowngymnospermgroup.The largest family of conifers is the Pinaceae, which contains

86 Plant diversity

the pines (Pinus), spruces (Picea), hemlocks (Tsuga), and firs(Abies).Coniferstypicallyproduceevergreen,needlelikeleaves,butthelarches(Larix)producedeciduousleaves.Coniferleaveshavemanytraits,suchasathickcuticle,sunkenstomata,andmodificationsofthexylem,thathelpthemsurviveinverycoldandverydryenvironments.

Thereareapproximately100speciesofPinus.TheyarenativetotheNorthernHemisphere,wheretheygrowinadiverserangeofhabitatsfromhotsemidesertstocoldmountainforests.Pinesproduceleavesinbundlescalledfascicles.Thenumberofneedlesperfasciclecanbeanimportanttraitfordifferentiatingspecies.Maleandfemaleconesareproducedonthesameplant.Maleconesaresmall,papery,andproducealargeamountofpollen.Theseed-producingfemaleconesarewoodyandrangeinsizefromseveralmillimeterstoseveralcentimetersinlength.Femaleconesoftenhaveuniquefeaturesthatcanbeusedtoidentifydif-ferentspecies.

Another important conifer family is Cupressaceae. Junipers(Juniperus), cedars (Cupressus), redwoods (Sequoia), and other

Table6.1 Major Groups of Living Gymnosperms


Cycadophyta cycads 130–150

Ginkgophyta ginkgos 1

Coniferophyta conifers 600–650

Gnetophyta gnetophytes 70–80


membersofthisfamilyarehighlyvaluedfortheirwood,whichisusedextensivelyintheconstructionindustryforshinglesandsid-ing.Otherspeciesarecommonlyusedasornamentalsinlandscap-ing.Somespecies,particularlyinJuniperus, producefragrantwoodthatisusedinmakingchestsandclosets.Cupressaceaeisanoldfamilywhoselineagedatesback248to206millionyears.Sequoia-dendron giganteum (giantsequoia)andSequoia sempervirens (coastredwood)ofCaliforniaaresomeofthelargesttreesonEarth.

The conifers listed previously are predominantly found inthe Northern Hemisphere. The families Podocarpaceae andAraucariaceae,ontheotherhand,arecommonintheSouthernHemisphere.Theseedsofthesefamiliesareoftenassociatedwitha fleshy structure that attracts birds. The monkey puzzle tree(Araucaria)producessomeofthelargesttreesinsoutherntropi-calforests.TheNorfolkIslandpine(Araucaria heterophylla)isacommonornamentalspecies.

CycadsCycadophyta is a very old lineage of tropical and subtropicalplantsthatevolved290to248millionyearsago.Theywereanextremelydiversegroup,buthave sincedwindled toapproxi-mately130–150speciesin11genera.

Cycadsproducelargeleavesthatareoftenmistakenforpalms. Like all gymnosperms, cycads reproduce using cones. Unlikeconifers, however, cycads produce male and female cones ondifferentplants.Theyarepollinatedbyinsects,predominantlybeetles,whichtransferpollenfrommaletofemaleconeswhilefeedingonpollenandother coneparts.Afterpollination, thepollentubegrowsintotheovuleandreleasesflagellatedspermthatswimtotheeggforfertilization.

GinkgosGinkgophyta evolved 260 million years ago.Althoughdiverseand widespread in the fossil record, only one species, Ginkgo

88 Plant diversity

biloba (ginkgo or maidenhair tree), still survives (Figure 6.4).Comparisonsoflivingplantstofossilsshowthatthisspecieshaschangedverylittleduringthepast100millionyears.

Ginkgos are attractive trees. Their deciduous fan-shapedleavesturnabrilliantyellowinautumn.Maleandfemaleconesareborneonseparatetrees.Afterpollination,thepollengrainsform highly branched pollen tubes that grow throughout theovuletissue.Oncethepollentubecontactsthearchegonium,it

Figure 6.4 Shown above are Ginkgo biloba leaves and female cones. Ginkgo biloba is an ancient gymnosperm species, whose extract is commonly used as a memory enhancer.


burstsandreleasestheflagellatedspermthatswimtotheeggforfertilization. The fleshy femaleginkgocones are infamous fortheirstench,resemblingacombinationofoldcheeseandfeet.Hence,mostornamentalplantingsconsistofmaletrees.

GnetophytesGnetophytesarequitedistinctinappearancefromoneanotherand other gymnosperms. Structural and genetic data stronglysupportGnetophytaasamonophyleticgroup.Thislineagecon-tainsthreegenera:Welwitschia, Gnetum,and Ephedra.

Welwitschia mirabilis,describedatthebeginningofthischap-ter,isthelonememberofthisgenus.PlantsinthegenusGnetumarewoodytropicalvineswhoseleavesresemblethebroadleavesofangiosperms.Thereareapproximately30Gnetum species.

Theremaininggenus,Ephedra(Mormontea)hasapproxi-mately 40 species, most of which grow in the arid regions ofthe western United States and Mexico (Figure 6.5). They aretypicallyshrubbyplantswithjointedphotosyntheticstemsandsmall, scalelike leaves. Ephedras produce the chemical ephed-rine,whichactsasastimulantandcanbeusedtotreatallergiesandrespiratorydisorders.

Living FossilsPaleobotanists recognized species of ginkgos and dawn redwoods from fossil records in which they were very abundant. In 1691, living ginkgo trees were “discovered” to Westerners by Engelbert Kaempfer, who found them growing in the temple grounds of Buddhist monks in China and Japan. In 1941, an unknown tree species was seen in a forest in China. In 1948, these trees were identified as dawn redwoods, previously believed to be extinct. Finally, in 1994, 39 trees of a gymnosperm species (Wollemia nobilis, Araucariaceae) thought to be extinct were found growing in a remote forest in Australia.

90 Plant diversity

Figure 6.5 Ephedra, commonly referred to as Mormon tea, are shrubby plants that grow in arid environments, such as Arches National Park in Utah (above). Mormon tea was used by Native Americans to make a stimulating drink.


Gnetophytesareofparticularimportancetobotanistsbecausethey share interesting similarities with flowering plants. Forexample,maleconesproducepolleninstructuresthataresimi-lartoanthersfoundinflowers.Likewise,modifiedleavescalledbracts are often associated with male and female gnetophytecones,muchthesamewaythatmodifiedleavesareassociatedwithflowers.Mostimportant,however,thereproductivepro-cessofgnetophytesisverysimilartothatofangiosperms.

In all other gymnosperms, the pollen grain produces twospermcells,onlyoneofwhichfertilizestheegg.Ingnetophytes,onespermfertilizestheeggandtheotherfuseswithanon-eggcellinthefemalegametophyte.Thissecondfertilizationformsa short-lived embryo that eventually degenerates, but it mayprovide some nourishment to the other developing embryo.Thisprocessoftwofertilizationeventsissimilartotheoneinangiosperms, and may suggest a common ancestor betweengnetophytes and angiosperms. Some structural data suggest,however,thatgnetophytesaremorecloselyrelatedtopinesandarenotancestorstotheangiosperms.

oRIGInsanDReLaTIonshIPsoFGymnosPeRmsFossilevidenceindicatesthatseedplantsfirstevolvedapproxi-mately 365 to 380 million years ago. The oldest known gym-nospermfossilsareofaplant in thegenusArchaeopteris. It isamemberofagroupreferredtoastheprogymnosperms, whichmeans“beforethegymnosperms.”Archaeopteriswasatreelike,woodyplant.Ithadleavessimilartofernfrondsandproducedseedsinsporangiaattachedtothebranches.Otherprogymno-sperm fossils have features indicating that they evolved fromseedlessvascularplants.Seedplantsevolvedfromtheseprogym-nospermancestors.

Several diverse lineages of seed-producing plants evolvedduring the 65 million years that followed. One group calledseed fernshadfernlikeleavesthatproducedseedsattheirtips.

92 Plant diversity

Another important group, the cordaites (Cordaitales), con-tainedtreesandshrubs thatresembledmodernconifers.Seedfernsandcordaitesbecameextinct290to248millionyearsago,butthey,alongwithlycophytesandcalamites,weredominantplantsbeforethattime.

Cycadeoids (Bennettitales) are another extinct gymno-spermlineage.Cycadeoidsareinterestingbecausetheyaretheonly gymnosperm lineage to produce cones containing bothmale and female structures. Cycadioids, cycads, and ginkgosevolved248to206millionyearsagoanddiversified206to144millionyearsago.Cycadeoidsbecameextinctapproximately65millionyearsago,butthetwootherlineagesexiststilltoday.Although theyhave lost someof theiroriginaldiversity, thishighlysuccessfulgroupofplantshasexistedformorethan145millionyears.

Becausesomeoftheearliestgymnospermlineagesareknownonly from fossils, there is uncertainty about the relationshipsamongthem.Severaldifferentphylogenieshavebeenproposedforlivinggymnosperms,eachwithitsownstrengthsandweak-nesses, depending upon the data used to construct the phy-logeny. As described earlier, some botanists have concludedthat gnetophytes are the gymnosperm lineage that shared themostrecentcommonancestortoangiospermsbecauseoftheirsimilar fertilization process (called the anthophyte hypothesis).Although there are compelling reasons that support this con-clusion,currentstructuralandgeneticdatasuggeststhatangio-spermsdivergedfromthegymnospermslineageveryearly,andthat gymnosperms continued to diversify (called the gne-pine hypothesis).Cycadsandginkgosarecloselyrelatedbasallineagesinthegymnosperms.Thepresenceofflagellatedsperminthesetwogroupsalsoindicatesthattheseareoldergymnospermlin-eages.Nonpine conifers compriseone remaining lineage, andPinaceae conifers and gnetophytes evolved from a commonancestor.


VaLueoFGymnosPeRmsGymnospermsareecologicallyimportantplantsthataredomi-nantspeciesinmanyecosystemsworldwide.Inadditiontopro-vidinghabitatandfoodforotherorganisms,theyalsoshapetheirenvironmentbyaffectingsoil,wateravailability,andtemperature.

Gymnospermshavesignificanteconomicvalue.Awidevari-etyofspeciesareusedinlandscaping.Otherspeciesaregrownforfuel,lumber,andpaperpulpproduction.Pinesinparticulararetappedforresins,whichcanbeconvertedintoavarietyofcommercial products including turpentine and rosins. In thepast,pineresinscallednavalstoreswereusedasawaterproof-ingagentforwoodenships.Afewgymnosperms,suchaspiñonpinesandjunipers,areevengrownforfoodandflavorings.

summaRyGymnospermsareseed-producingvascularplants.Seedsandpol-lenareproducedinconescomposedofsporophyllsorconescales.Gymnospermsarosefromseed-producingancestorsthatevolvedmore than 365 million years ago. Gymnosperm lineages, suchas the seed ferns, cordaites, andcycadeoids,were large,diversegroupsthathavesincebecomeextinct.Conifers,cycads,ginkgos,andgnetophytesarethefourlivinggymnospermlineages.

Every tree is a HypothesisA fundamental component of the scientific method is the developing and test-ing of hypotheses. In systematics, the hypothesis is the phylogeny developed by a systematist. Because it is impossible to actually observe the entire evo-lutionary history of a group of plants, systematists develop a phylogeny based on their interpretations and conclusions from the data they collected. Other systematists can then collect and analyze additional data to test the relation-ship proposed in the original phylogeny or propose new relationships.

94

FloweringPlantsTheangiosperms

The rapid development . . . of all the higher plants within recent geological times is an abominable mystery.

—Charles Darwin (1809–1882)English naturalist

The passage on the previous page is from a letter written by Charles Darwin to his colleague, the eminent botanist SirJosephHooker.The“abominablemystery”Darwinreferredtowasthesuddenanddramaticappearanceanddiversificationofangiospermsinthefossilrecord.Fossilsofothermajorgroupsofplants showapatternof lineagesappearinggraduallyanddiversifyingslowlyoverthecourseofhundredsofmillionsofyears. Angiosperms made their first appearance in the fossilrecordapproximately135millionyearsago.Angiospermsthenunderwent a rapid proliferation and diversification 70–100millionyearsago.By60millionyearsago,amajorityof themodernangiospermfamiliesthatexisttodaywerewellestab-lished.Noothergroupofplantshasshownsuchrapidevolu-tion, diversification, and dominance of the landscape in thehistoryofEarth.

The successof theangiospermswasmadepossible largelythroughtheuniquefeaturesthatresultedfromtheevolutionofflowersandfruits.Asurveyofthemorethan250,000speciesofangiospermsrevealsanastonishingarrayofflowerandfruitstructuresandmodifications.Anotherevolutionaryadvantageof angiosperms is their diversity of growth forms and veg-etativetraits.Angiospermsrangefromminuteaquaticplants,

96

FloweringPlantsTheangiosperms

Say it With Flowers“O, my love’s like a red, red rose....” The Scottish poet Robert Burns, and mil-lions of other romantics past and present, have associate red roses with true love. Throughout history, flowers and fruits have been associated with emo-tions and other things in what is called “The Language of Flowers.” Acorns are a symbol of immortality. Foxgloves represent insincerity. Yellow poppies and corn symbolize success and riches. Several nations are also associated with flowers: peonies with China, lilies with France, and thistles with Scotland.

97Flowering Plants

suchaswatermeal(Wolffia),toagiantquakingaspen(Populus tremuloides) clonethatcovers106acresandisthelargestorgan-ismonEarth.TheirabilitytoadapttotheirenvironmenthasallowedangiospermstohaveanamazingimpactontheecologyandevolutionoflifeonEarth.Angiospermsareanimportantresourcetohumans,astheyhavebothpracticaluseandculturalsignificance.

TheFLoWeRThe word angiosperm comes from the Greek words angeion(“vessel”) and sperma (“seed”), and refers to the fact that

Figure 7.1 A typical flower consists of sepals, petals, stamens, and one or more carpels.

98 Plant diversity

angiosperms produce seeds from ovules that are completelyenclosed in sporophyte tissue. This is in contrast to gymno-sperms,whichproduceseedsfromabareovule.Specifically,theangiospermvesselisthewalloftheovarythatenclosestheseed.Thepresenceofflowersthatproducetheseseed-enclosedfruitsisadefiningcharacteristicofangiosperms.

Flowers consist of four parts (sepals, petals, stamens, andcarpels)thatarearrangedintofourgroupscalledwhorls(Fig-ure7.1).All fourwhorlsattach toastructureat thebaseofthe flower called the receptacle. The outermost whorl, orcalyx, iscomposedofgreen, leaflikesepals,whichcoverandprotect the developing flower bud. The petals of the flowermake up the next whorl, which is called the corolla. Petalsmayresembleleaves,butunlikeleaves,theyareoftenbrightlycolored,attractingpollinatorsforsexualreproduction.Sepalsandpetalsthatcannotbedistinguishedfromoneanother,asis the case with tulips and cacti, are called tepals. The calyxand corolla are called the sterile whorls because they do notproducegametes.

The stamens and carpels make up the two fertile whorls,which produce the gametes required for sexual reproduction.The stamensmakeup the thirdwhorl,which isknownas theandroecium(meaning“malehouse”).Pollencontainingthemalegamete(sperm)isproducedintheantherofthestamen,whichissupportedonastalkcalledthefilament.Theinnermostwhorlof a flower is the gynoecium (meaning “female house”), whichiscomposedofthecarpels.Carpelsaremadeofastigma,style,andovary.Thecarpelisalsocalledthepistil.Agynoeciummayconsistofoneormorecarpels.Agynoeciumcomposedoftwoormorecarpelsfusedtogetherisacompound pistil.Theovaryofthegynoeciumeventuallymaturestoformafruitcontainingoneormoreseeds.

Flowersaregroupedtogetheronaplanttoformaninflores-

cence (Figure7.2).Aninflorescencecanbecomposedofasingle

99Flowering Plants

flower(solitaryinflorescence),oranynumberofdifferentmulti-floweredinflorescences.Thestalkthatsupportsaninflorescence,whether multi-flowered or solitary, is called thepeduncle. Thestalkthatsupportsanindividualflowerwithinamulti-floweredinflorescenceiscalledthepedicel.

Figure 7.2 Shown above are the basic types of inflorescences. Inflo-rescence refers to the way in which individual flowers are arranged on the stem.

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anGIosPeRmLIFecycLeThelifecycleofalilyservesasagoodexampleoftheangiospermalternationofgenerations.Itbeginswiththegerminationofaseed,whichisthesporophytegeneration.Theseedlingdevelopsintoamatureplantthatwilleventuallyformflowers.Mostflow-erscontainbothstamensandcarpels.Insomeangiosperms,sta-mensandcarpelsareproducedinseparateflowersonthesameordifferentplants.

Withintheantheronthestamen,sporemothercellsundergomeiosistoformhaploidspores.Eachsporedevelopsintoapol-lengraincontainingatubecellandagenerativecell.Whenthepollengraingerminatesonthestigma,thetubecellcontrolsthegrowth of the pollen tube. This tube grows through the styletowardtheovary,carryingwithitthegenerativecell.Thegen-erativecelldividestoformtwospermcells.Thegrowingpollentubeisthemalegametophyte.

Within the carpel, spore mother cells undergo meiosis toformfourhaploidspores.Threeofthehaploidsporesdegener-atewhileonedivides threemore times toproduce the femalegametophyte.Theangiospermfemalegametophyteiscomposedof seven cells. The large central cell contains the two haploidpolarnuclei.Threecellsaretheantipodalsandtwocellscalledthesynergids arenexttotheegg.Thesesevencellsandeightnucleimakeupthematurefemalegametophyteand,withtheintegu-mentlayersaroundit,formtheovule.Ovulesareenclosedandattachedtothesporophytetissuesoftheovary.Thus,thefemalegametophyteisphysicallyattachedto,andnutritionallydepen-dentupon,thematuresporophyte.

Akeyfeatureoftheangiospermlifecycleisthereductionofthegametophytestage,particularlythefemalegametophyte,andelaborationofthesporophyte.Thisisexactlytheoppo-site of what occurs in bryophytes, where the sporophyte isattachedto,andnutritionallydependentuponamuchlargergametophyte.

101Flowering Plants

DouBLeFeRTILIzaTIonWhenthepollentubereachestheovule,itreleasesthetwospermcells.Onespermcellfuseswiththeeggtoformthezygotethatwill eventually become the next sporophyte. The other spermcellfuseswiththetwopolarnucleitoformtheendosperm,whichprovidesfoodforthedevelopingzygote.Thisdouble fertilizationisauniquefeatureoftheangiospermlifecycle.

Following the formationof the zygote andendosperm, theovuledevelopsintotheseedthatcontainstheplantembryoandfoodreserves,whichmaybeintheformofendospermorsugarsand starches stored in modified leaves called cotyledons. Ripeovary tissues surrounding the seed form the fruit. Ultimately,theseedisdispersedfromtheplantthroughavarietyofdifferentmechanisms.Somefruitsarefleshyandcontainsugars,lipids,orothersubstancestoenticeanimalstoeatthefruitandinternallytransporttheseeduntilitpassesthroughthedigestivetract.Oth-ershavehooks,barbs,orotherdevicesthatattachtotheoutsideof animals to disperse the seed. Once dispersed, the seed willgerminateandformthenextsporophyte.

majoRanGIosPeRmGRouPsIn 1703, English botanist John Ray divided angiosperms intomonocots (plants whose seeds have one cotyledon) and dicots

Pollination by deceptionFlowers use different combinations of color, scent, and shape to attract pol-linators. Some of the most specialized flower pollinator relationships involve orchids, whose flowers mimic the color, shape, and even scent of females in the bee and wasp species that pollinate them. Male bees and wasps, lured in by the false promise of a mate, inadvertently transfer pollen from one flower to another. Some arums (plants of the family Araceae) use a similar strategy, mimicking the stench of rotting meat. Flies, seeking a place to deposit their eggs, pollinate the flowers.

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(plantswhoseseedshavetwocotyledons).Botanistshavetra-ditionally followed this classification and continued to divideangiosperms into the Magnoliopsida (dicots) and Liliopsida(monocots)basedonavarietyoftraits,suchasthearrangementofvascular bundles(Figure7.3)andfeaturesofroots,leaves,andflowers.

Recentstudies,however,haveshownthatthedicotsareanartificial grouping of several different lineages. Some plantspreviouslyclassifiedasdicotsareactuallyancientangiospermlineagesthatarenowcollectivelyreferredtoasthebasal angio-

sperms (Table 7.1). This group consists of several families,includingtheAmborellaceae,Nymphaeaceae,andIlliciaceae.The remaining angiosperms are now referred to as the core

Table7.1 Major Groups of Living Angiosperms


Amborellaceae

Nymphaeaceae

Autrobaileyales basalangiosperms 170

Nymphaeaceae,

Illiciaceae

Magnoliopsida* magnoliids 9,000

Liliopsida monocots 70,000–72,000

Magnoliopsida* eudicots 175,000–180,000

*Magnoliopsidaisthetraditionalnamegiventodicots.Atpresent

thereisnoICBNnamefortheseparatemagnoliidoreudicotclades.

103Flowering Plants

angiosperms. Thisgroupincludesthreemonophyleticlineages:magnoliids, eudicots, and monocots. The magnoliid cladecontains several ancient angiosperm families, including the

Figure 7.3 Cross-sections of monocot and dicot stems reveal the differ-ences in vascular bundle arrangement. Vascular bundles are arranged in a ring in dicots (a), but scattered in the monocot stem (b).

a

b

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magnolias (Magnoliaceae), laurels (Lauraceae), spicebushes(Calycanthaceae), and black peppers (Piperaceae). Eudicots

(true dicots) make up a large, natural group that containsabout 75% of all dicot species. Eudicots share a commonfeaturethatisnotfoundinanyotherfloweringplants:Theyhavethreeopeningsintheirpollengrainwalls.Allotherplants(gymnosperms, basal angiosperms, magnoliids, and mono-cots)producepollengrainsthathaveonlyoneopeningintheirwalls.Beyond thisdifference,magnoliidsandeudicots sharemanyotherfeatures(Table7.2).

Despitechangesinourunderstandingofdicots,monocotsarestillrecognizedasasinglelineagethatdescendedfromacom-monancestor.Monocotsaccountforapproximately22%ofallangiosperms.

Table7.2 Differences Between the Three Core Angiosperm Groups

Trait Monocots Magnoliids Eudicots

Cotyledons 1 2 2

Vascularbundle scattered ring ring

arrangementinstem

Leafveinpattern parallel pinnate palmate,

pinnate

Numberofflower three-merous many four-merous,

parts five-merous

Openingsin 1 1 3

pollengrains

105Flowering Plants

Significantdifferencesexistbetweenthefloralstructuresofeudicotsandmonocots.Ineudicotflowers,thepartsofthedif-ferentfloralwhorlsaretypicallyinmultiplesoffour(four-merous)orfive(five-merous).Forexample,membersofthemustardfam-ily(Brassicaceae)produceflowerswithfoursepals,fourpetals,and four stamens.Species in the rose family (Rosaceae), suchas roses, strawberries,andblackberries,have flowerswith fivesepalsandfivepetals.Monocotflowers,suchasirises,lilies,andtulips,arethree-merous,withthreesepals,threepetals,threeorsixstamens,andapistilwiththreecarpels.

ecoLoGIcaLanDeconomIcVaLueAngiospermsaredominantcomponentsofterrestrialenviron-mentsworldwideand,consequently,playamajorroleintheeco-logicaldynamics thatmaintainahealthyplanet.Angiospermsalsoincludemanyimportantresourcesthathumansdependonforavarietyofpurposes.Angiospermsprovidefood,ornamen-tals,fibers,andawidearrayofchemicals.

Oaks(Fagaceae),hickories(Juglandaceae),andmaples(Sap-indaceae)aremajorcomponentsof forests inmanytemperateareas. Tropical forests, however, are often dominated by treesfrom a multitude of different families, including dipterocarps(Dipterocarpaceae), laurels (Lauraceae), and figs (Moraceae).Trees in these families support numerous other life forms inforestecosystemsbyprovidingfoodandhabitats.Manyofthesefamiliesalsoprovidetimberandotherresourcesforhumans.

Therosefamily(Rosaceae)iswellknownforitsornamentalspecies, like roses (Rosa sp.) and cinquefoil (Potentilla), andalsoforitsediblespecies(Figure7.4),likeapples(Malus),andpears(Pyrus),andpeaches,plums,andcherries(allinthegenusPrunus).

Thebeanfamily(Fabaceae)isoneofthelargestangiospermfamilies. Members of Fabaceae are also called legumes, whichreferstotheuniquefruitproducedbyspeciesinthisfamily.The

106 Plant diversity

symbioticrelationshipsbetweenlegumesandnitrogen-fixingsoilbacteriagivelegumeseeds(beansandpeas)ahighproteincon-tent,makingthisanagriculturallyimportantfamily.Speciessuchasbeans(Phaseolus vulgaris),soybeans(Glycine max),fieldpeas(Vicia faba),andlentils(Lens culinaris)contributetothedietsofhumansandwildlifeworldwide.

a b

c d

Figure 7.4 The rose family includes many edible fruits. Pictured above are two ripened apples (a), peaches ready to be picked (b), ripe cherries (c), and fresh pears (d).

107Flowering Plants

Themint family(Lamiaceae) includesmanyculinaryherbsandplantsrenownedfortheirperfumes.Theflavorsandscentsof plants in the mint family come from glands on the leaves,whichproducearomaticoils.Basil(Ocimum basilicum), laven-der(Lavandula), mint(Mentha), oregano(Origanum vulgare), patchouli(Pogostemon cablin),sage(Salvia officinalis),rosemary(Rosmarinus officinalis),andthyme(Thymus)arevaluedherbsinLamiaceae.Catnip(Nepeta),coleus(Plectranthus),andbeebalm(Monarda)arepopularornamentals.

Thenightshadefamily(Solanaceae)containsmanypoisonousplants. The poisons are often powerfulalkaloids, which have arangeofeffects. Tobacco (Nicotiana),belladonna(Atropa),andjimsonweed(Datura)producealkaloidswithnarcoticeffects.Hotpeppers(Capsicum)get theirheat fromthealkaloidcapsaicin.Importantedibleplants, including tomato(Solanum lycopersi-cum)andpotato(Solanum tuberosum),arealsointhisfamily.

Thesunflowerfamily(Asteraceae)isthelargestofalleudicotfamilies,withmorethan25,000species.Itcontainsmanycom-merciallyimportantspecies,suchastheannualsunflower(Heli-anthus annuus),whichisgrownforitsseeds,oil,andflowers.Thisfamilyalsocontainscommerciallygrownornamentals, includ-ing dahlias (Dahlia), mums (Chrysanthemum), and marigolds(Tagetes),aswellasaggressive,noxiousweeds,suchasdandelion(Taraxacum officiale)andCanadathistle(Cirsium arvense).

Thegrasses(Poaceae)accountforapproximately17%ofallangiosperms. This monocot family serves as the foundation offoodwebsandotherprocessesinprairies,savannas,andtundraecosystems. Grasses can be found in most other ecosystems aswell.Nineofthetop20cropspeciesaregrasses,withcorn(Zea mays),wheat(Triticum aestivum),andrice(Oryza sativa)provid-ing50%ofhumancaloricintake.Bamboos(Bambusa)aregrassesthathaveawiderangeofuses, includingconstruction,textiles,and papermaking. Other species, such as cheat grass (Bromus tectorum) and Johnson grass (Sorghum halapense), are invasivespeciesthathaveadetrimentaleffectonnativevegetation.

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Theirises(Iridaceae),orchids(Orchidaceae),andlilies(Lili-aceae) are often called the “showy monocots” because of thebright,colorfulpetalsintheirflowers(Figure7.5).TheIridaceaeincludesirises(Iris),gladiolus(Gladiolus),crocus(Crocus), andblue-eyedgrass(Sisyrynchium).TheanthersfromCrocus sativus

a

b c

Figure 7.5 The lilies, irises, and orchids produce bright, showy flowers. Photographed above are the white lily (a), purple iris (b), and the harle-quin “dancing lady” orchid (c), also known as a butterfly plant.

109Flowering Plants

arethesourceofthespicesaffron.Orchidsarethelargestangio-spermfamily,withmorethan30,000species.Thereareterrestrialorchidsaswellasmanyepiphytes, plantsthatgrowonthestemsandbranchesoftrees.Orchidsareparticularlydiverseinthetrop-ics,wheretheyformcloserelationshipswiththeorganismsthatpollinatetheirflowers.Liliaceaecontainsornamentalsincludinglilies(Lilium)andtulips(Tulipa).Thereareseveralediblelilies,includingonion(Allium cepa),garlic (Allium longicuspis),andchives(Allium schoenoprasum).

oRIGInsanDReLaTIonshIPsoFanGIosPeRmsThe oldest angiosperm fossils are flowers and pollen that are130–140millionyearsold.TheoldestcompletefossilplantisinthegenusArchaefructus thatlivedmorethan125millionyearsago. Itwasasimpleplantwhoseflowershadnosepalsorpetals,butnumerousstamens.

One of the first hypotheses about the origins of floweringplantswasdevelopedbyEnglerandPrantl,whosuggestedthatAmentiferae,agroupintheirclassification,wasthemostprimi-tiveangiospermgroup.This conclusionwasbasedon the factthatmanyofthesetreesarewindpollinated,justlikethemoreprimitivegymnosperms.Otherresearchersconcludedthatfami-liessuchasMagnoliaceae(magnoliafamily)andRanunculaceae(buttercupfamily)werethemostprimitivebecausetheirflow-ers contain many parts. Recent genetic analyses have shown,however,thatneitherofthesefamiliesarerepresentativeoftheoldesttypeofangiosperm.Magnoliaceaeisanancientfamily,butitisnottheoldest,andRanunculaceaehasbeenshowntobeamemberoftheeudicots.

Currently,manybotanistsagree that the familiesAmborel-laceae, Nymphaeaceae, Trimeniaceae, and the order Illicialesaretheoldest living lineagesof floweringplants.Thesegroupsproduce small, simple flowers that have few parts and simplepollinationmechanisms.Collectively,theseancientgroupsform

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thebasalangiosperms.Fossilevidencealsoindicatesthatthefirstangiospermshadsmall,nondescriptflowerswithfewfloralparts.ThespeciesAmborella trichopoda(Amborellaceae)isashrubbyplant thatgrows inthe cloudforestsofNewCaledonia.Manystudieshave indicated that it is likely the living descendentoftheoldestangiospermlineageonEarth.Fossilandgeneticdataindicate that monocots, magnoliids, and eudicots diverged asseparatelineagesapproximately100millionyearsago.

anGIosPeRmsuccessAngiospermshaveevolvedanddominatedtheterrestrialenvi-ronmentlikenoothergroupofplants.Theflowerundoubtedlyisaprimaryreasonforthissuccess.Flowersenabledplantstousedifferentshapes,colors,andscentstoattractpollinators.Flowersalsofrequentlyprovideafoodrewardofpollenornectartopolli-natorsinreturnfortheserviceofvisitingflowersandtransferringpollen.Theevolutionanddiversificationoftheseinsectandbirdpollinatorsislinkedtothatoftheangiosperms.

Likeflowers,fruitsprovideafoodrewardtoanimalsthateata fruit and disperse the enclosed seeds. Fruit size, shape, andcolorhaveevolvedinresponsetonaturalselectionmediatedby

Big FlowersThe brownish-orange flowers of the giant rafflesia (Rafflesia arnoldi ) are the largest single flowers of any angiosperm. A typical Rafflesia flower can be up to 3 feet (1 m) across and weigh as much as 25 pounds (11 kg). The titan arum (Amorphophallus titanium) produces the largest inflorescence. Its flowers are very small, but they combine to form a special type of inflo-rescence called a spadix. Separate male and female flowers are attached to a central column that can be 3 to 6 feet (1 to 2 m) tall. A huge modified leaf surrounding the column gives the spadix the appearance of being a single large flower.

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theanimalsthateatanddispersetheseeds.Angiospermshaveevolvedanarrayofmechanismstodispersetheiroffspring.

Changes in the life cycle have also promoted angiospermevolution.Whiletheotherseedplants,gymnosperms,cantakeaslongastwoyearstoprogressfrompollinationtothereleaseofthematureseed,angiospermshaveacceleratedtheprocess.Pollina-tion,fertilization,andmaturationoftheseedcanoccurwithinamatterofdaysormonths.Thisaccelerationmaybeduetothenutritionalbenefitsoftheendospermforthedevelopingembryo.Angiospermsarealso theonlyseedplants tohaveevolvedtheannuallifecycleinwhichaplantcompletesitslifeinonegrow-ing season. By shortening different aspects of their life cycle,angiospermscanreproducemorequickly,therebyspeedingtheirresponsetonaturalselectionandacceleratingtheevolutionandspreadofadaptivetraits.

summaRyAngiospermsarevascularplantsthatproduceseedsfromflow-ersandenclose theseeds ina fruit.Angiospermsare themostrecently evolved group of plants, and they dominate the ter-restrial environment. The flower and fruit are key traits thatallowedangiospermstointeractwithanimalpollinatorsandseeddispersersand,consequently,undergoextensivediversification.Therearethreemajorgroupsofangiosperms:basalangiosperms,monocots,andeudicots.Manyspeciesinthesegroupsareeco-logicallyandeconomicallyimportant.

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Algae AgeneraltermforphotosyntheticmembersofthekingdomProtista.

Alkaloid Atypeofchemicalproducedbycertainplantsthatismadeoutofnitrogenandcanbetoxicwheningested.

Alternation of generations Alifecyclethatalternatesbetweenamulticel-lularhaploidgenerationandamulticellulardiploidgeneration.

Anatomy Thestudyofanorganism’sstructure.

Androecium Themalepartsofaflower.

Angiosperms Plantsthatproduceflowersandwhoseseedsarecontainedwithinafruit.

Animalia Theanimalkingdom.

Annulus Athickenedbandofcellsonafernsporangium,whichisinvolvedinthedispersalofspores.

Anther Floralstructureinwhichpollenisproduced.

Antheridia Malereproductivestructuresthatproduceandprotectsperm.

Antipodals Thethreecellsofthefemalegametophytethatareclusteredattheendoppositetheegg.

ArbusculesSpecializedstructuresformedbymycorrhizalfungiinsideaplantcellthatenabletheplantandfungustoexchangenutrients

Archaea Thekingdomofprokaryoticunicellularorganismscontainingblue-greenalgae,methane-producingbacteria,andotherprimitivelifeforms.

Archegonia Thefemalereproductivestructuresthatproduceandprotecttheegg.

Artificial classification system Asystemofgroupingorganismsthatisbasedonarbitraryfeaturesrathertrueevolutionaryrelationships.

Asexual reproduction Formationofoffspringthatdoesnotinvolvethejoiningofeggandsperm.

Ascus (plural: asci) Asaclikecellinwhichascomycetesformspores.

Ascocarp Thefruitingbodyofanascomycete.

Autotrophs Organismscapableofsynthesizingitsownenergy.

Bacteria Agroupofunicellular,prokaryoticorganisms.

Basal angiosperms Anamegiventothemostprimitiveangiospermlineages.

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Basidium (plural: basidia) Theclub-shapedstructureinwhichbasiomyce-tesformspores.

Basidiocarp Thefruitingbodyofabasidiomycete.

Binomial nomenclature ThesystemdevelopedbyLinnaeusinwhicheachspeciesisgivenanameconsistingoftwowords:thegenusnameandthespeciesname.

Biodiversity ThediversityoflifeonEarth.

Blades Theflattenedphotosyntheticregionsofaleaforalgae.

Bracts Modifiedleaflikestructuresthatcanbepartofaflowerorfruit.

Brown algae Groupofmulticellularalgaeusuallyfoundinmarineenvironments.

Bryophytes Non-floweringplantsthatincludemosses,liverworts,horn-worts,andquillworts.

Bud Smallembryonicfloralorvegetativeshoots.

calamites Ancientgroupofhorsetails.

calyx Theoutermostfloralwhorlconsistingofallofaflower’ssepals.

capsule Aspore-containingstructureofthemosssporophyte.

carotenoids Aclassofyellowandorangepigments.

carpels Theovule-encasingstructuresthatmakeupthegynoecium.

cellulose Themaincomponentofcellwallsinplants.

central cell Thecellintheangiospermfemalegametophytethatcontainstwohaploidnuclei;itbecomesendospermafterfusionwithsecondspermnucleus.

chitin Asubstancethatformsthecellwallsofcertainfungi.

chlorophyll Agreenpigmentresponsibleforcapturingthelightusedinphotosynthesis.Therearetwotypesofchlorophyll,aandb, whichhaveslightdifferencesinthewavelengthsoflighttheyabsorb.

chloroplasts Structureswithinplantcellsthatcontaintheenzymesandpigmentsnecessaryforphotosynthesis.

chromosomes TheorganizedstructuresofDNAinacell.

clade Agroupconsistingofanancestorandallofitsdescendants.

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cladistics Thesystemofgroupingorganismsbasedonananalysisoftheirprimitiveandadvancedtraits.

classification Theprocessoforganizinggroupsintoahierarchicalsystem.

common name Theunofficialnamegiventoaplantbythosewholivenearit.

compound pistil Agynoeciumcomposedoftwoormorecarpelsfusedtogether.

cone Areproductivestructurethatproduceseitherpollenorseeds,typ-icallyfoundingymnospermsandothergroupsofnonfloweringplants.

cone scale Anindividualunitofthegymnospermstrobilus.

core angiosperms Groupingsthatincludethreemonophyleticlin-eages:magnoliids,eudicots,andmonocots.

corm Adryundergroundstructurefoundinperennialplantssuchasgladiolus.

corolla The(usually)conspicuously-coloredflowerwhorlconsistingofalloftheflower’spetals.

cotyledon Aleafthatprovidesnourishmenttotheplantembryodur-inggermination.

crozier Thecoiledleafofafern.

crustose Alichengrowthformthatresemblesacrustonthesubstrateuponwhichitgrows.

cuticle Awaxy,protectivelayerontheoutersurfacesofleaves.

deciduous Aplantthatlosesitsleavesduringautumnorthedryseason.

dendrograms Treelikediagramsthatillustraterelationships.

dichotomous key Alist ofpaired,contrastingstatementsusedtoiden-tifyanunknownorganismbytheprocessofelimination.

dicots Ageneraltermgiventoangiospermswhoseseedsproducetwocotyledons,nowdividedintotwogroups,thebasalangiospermsandtheeudicots.

dikaryotic Cellsinfungithathavetwohaploidnuclei.

diploid Havingtwofullsetsofchromosomesineachcell,characteristicofthesporophytegeneration.

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diversity Ameasureofthenumberandrelativeproportionofdifferentspeciesinacommunity.

domain Thetaxonomiclevelabovekingdom.

double fertilization Atwo-fertilizationevent,characteristicofangio-sperms,whereinonespermfuseswiththeeggtoformthezygoteandasecondspermfuseswiththepolarnucleitoformtheendosperm.

Endosperm Thetissuesformedduringadoublefertilizationeventthatnourishthegrowingangiospermembryo.

Epiphytes Nonparasiticplantsthatgrowontrees.

Ethnobotanists Scientistswhostudythewaysinwhichindigenouspeoplesuseplants,particularlyformedicinalpurposes.

Eudicots Thelargestgroupofangiosperms;theyhavetwocotyledonsandthreeopeningsintheirpollengrains.

Eukaryotic Organismswhosecellscontainnucleiandmembrane-boundorganelles.

Evergreen Atreewhoseleavescanbeshedatanytimeofyear,butneverallatonce.

Evolution Achangeingenetically-basedcharacteristicsofaspeciesthroughouttime.

Fascicles Bundlesofpineneedles.

Fertile whorls Thewhorlsofaflowerthatproducegametes.

Fertilization Thejoiningofeggandsperminsexualreproduction.

Fiddlehead SeeCrozier.

Field guide Abookthatcontainssimpledescriptionsandillustrationsofplantsinanarea.

Filament Thestalkofastamen.

Five-merous Aflowerthatcontainspartsinmultiplesoffive.

Flagella Tail-likestructuresthatpropelmanyeukaryoticcells,includingsperm.

Flavonoids Aclassofpigmentsfoundonlyinplantsandafewalgae.

Float Theinflatedpartofakelpbody.

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Flora Aguidewithdescriptions,illustrations,distributionsmaps,andkeysthatallowtheusertoidentifyplantsofaparticulargeographicalarea.

Flowers Thereproductivestructuresofangiospermscomposedofsepals,petals,stamens,andcarpels.

Foliose Alichengrowththatresemblesleaves.

Food webs Aninterlockingsystemofproducersandconsumersinanecosystem.

Four-merous Aflowerthatcontainspartsinmultiplesoffour.

Fronds Fernleaves.

Fruit Thematureseed-containingovary(orgroupofovaries)ofangiosperms.

Fruticose Alichengrowthformthatishighlybranchedanderect.

Fungi Thekingdomoforganismsthathavecellwallsandobtaintheirfoodthroughabsorption.

Gamete Ahaploidreproductivecell,eitherspermoregg.

Gametophyte Thehaploid,gamete-producingstageinthealternationofgenerations.

Gemmae (singular: gemma)Smallmassesofvegetativetissuethatformontheuppersurfaceofathallusthatcanbedispersedforasexual,vegeta-tivereproduction.

Generative cell Thecellinapollengrainthatdividestobecometwospermcells.

Genus Thetaxonomicrankbelowfamilyandabovespecies.

Germination Theresumptionofgrowthbyadormantspore,seed,orpol-lengrain.

Gills Theplatesontheundersideofthecapsofbasidiomycetefungi.

Green algae Thegroupofalgaethatgaverisetoplants.

Gymnosperms Plantsthatreproduceusingconesandbearexposed“naked”seeds(thatis,notcontainedinfruits).

Gynoecium Thecollectivetermforallofthecarpelsinaflower.

Haploid Havingonlyonesetofchromosomes.

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Herb Anonwoodyplant.

Herbarium Aplacewherepreservedplantmaterialsarestoredforstudy.

Herbarium sheets Piecesofpaperuponwhichpressed,driedplantspeci-mensaremounted;theytypicallyprovideinformationsuchastheplant’sscientificnameandwhereandbywhomitwascollected.

HeterosporyTheproductionoftwotypesofspores:microsporesthatgiverisetomalegametophytesandmegasporesthatgiverisetofemalegametophytes.

Heterotrophs Organismsthatmustobtainenergybyconsumingotheranimals.

Holdfast Partofthealgalbodythatattachesthealgatothesubstrate.

Homospory Theproductionofonetypeofspore.

Hydroids Primitivewater-conductingcellsinmosses.

Hyphae (singular: hypha) Fungalfilaments.

indusium Aprotectiveflapthatcoversimmaturesoriinferns.

inflorescence Aclusterofflowersclosetooneanotheronastem.

integuments Protectiveouterlayersthatsurroundthesporangiumofanovule.

international Botanical congress Thegoverningbodythatestablishesrulesonbotanicalnomenclature.

international code of Botanical nomenclature (icBn) Theinternation-allyagreeduponsetofrulesthatgovernthenamingofplants.

Kingdom Thetaxonomiclevelbelowdomain.

LeavesTheflattenedphotosyntheticpartsofavascularplant.

Legumes Fruitsthatarecharacteristicofthebeanfamily.

Leptoids Primitivefood-conductingcellsofmosses.

Lichen Organismthatresultsfromasymbioticrelationshipbetweenafun-gusandanalga.

Lignin Acomponentofthehardenedcellwallinxylem,theprimarycom-ponentofwood.

Mating types Geneticallydifferentformsofalgaecapableofsexuallyreproducingwithoneanother.

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Megaphylls Largeleaveswithmanyveins.

Megasporangium Astructureinwhichsporesareformedthatwillbecomeafemalegametophyte.

Megaspores Sporesthatgiverisetothefemalegametophyte.

Meiosis Theprocesswherebyadiploidcelldividestwicetoproducefourhaploidcells.

Microphylls Generallysmallleaveswithasinglevein.

Micropyle Asmallopeningintheseedplantovulethatthepollentubeentersforfertilization.

Microsporangium Astructureinwhichsporesthatwillbecomethemalegametophyteareformed.

Microspores Sporesthatwillgiverisetothemalegametophyte.

Mitosis Theprocesswherebyonediploidcelldividesoncetoproducetwoidenticaldiploidcells.

Monocots Angiospermswhoseseedscontainasinglecotyledon.

Monophyletic group Agroupcomposedofanancestorandallofitsdescendants.

Morphology Thestudyofthestructureandformoforganisms.

Mutualism Arelationshipthatbenefitsbothparticipatingspecies.

Mycelium Amassoffungalhyphae.

Mycology Thestudyoffungi.

Mycorrhizae Fungithatengageinsymbioticrelationshipswithplantroots.

natural classification system Asystemofgroupingorganismsthatisbasedontheirevolutionaryrelationships.

natural selection Aprocessofevolutionarychangethatoccurswhengeneticchangeproducesindividualswithgreaterreproductivesuccessorgreatersurvival.

nitrogen fixing Processofconvertingnitrogenfromagasintoabiologi-callyusefulform.

nucleus PartofaeukaryoticcellthatcontainsDNA.

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organelles Small,specializedstructureswithinaeukaryoticcell.

ovary Theenlarged,seed-producingportionofaflowerthat,afterfertil-ization,becomesafruit.

ovules Structuresinseedplantsthatcontainthefemalegametophyte.

Pedicel Thestalkofasingleflowerinaninflorescence.

Peduncle Thestalkofasolitaryflowerorinflorescence.

Perennials Plantsthatliveformorethantwoyearsandtypicallyreproducerepeatedlythroughouttheirlives.

Petals Thepartsofaflowerthatareoftenbrightlycolored.

PetioleThestalkofaleafthatattachesthebladetothestem.

Phloem Tissuethattransportssugarsandotherproductsofphotosynthe-sisthroughoutthevascularplantbody

PhotoautotrophsOrganismscapableofformingtheirownenergyresourcesthroughphotosynthesis.

Photosynthesis Theprocessthroughwhichplantsconverttheenergyinlightintosugarsandoxygen.

Phycobilins Agroupofreddishpigmentsfoundinredalgaeandblue-greenalgae.

Phycology Thestudyofalgae.

Phylocode Anomenclaturesystemthathasnohierarchicalrankingsandrecognizesonlyclades.

Phylogeny Theevolutionaryhistoryofanorganismorgroupoforganisms.

Pistil Thecollectivetermforthefemalepartsofaflower.

Plantae Theplantkingdom.

Polar nuclei Thetwonucleilocatedinthefemalegametophyteofangio-sperms,whichfusewithaspermtoformtheendosperm.

Pollen Astructurecontainingthespermcellsinangiospermsandgymno-sperms.

Pollen tube Atubethatdevelopsfromapollengrainandcarriesthespermtotheegg.

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Pollination Inangiosperms,thetransferofpollenfromananthertoastigma;ingymnosperms,thetransferofpollenfromamaleconetoafemalecone.

PollinatorsOrganismsthattransferpollenfromoneflowertoanother.

Polynomial Anoutdatedsystemofassigninganameofmultiplepartstoonespecies.

Progymnosperms Agroupofnow-extinctplantsthatgaverisetogymnosperms.

Prokaryotic Organismswhosecellslacknucleiandmembrane-boundorganelles.

Protista Theprotistkingdom.

Protonemas Thethreadlikegametophytesofsomenonvascularandseed-lessvascularplants.

receptacleThestructureinaflowerwherethefloralwhorlsattach.

red algae Alargegroupofmostlymulticellularmarinespeciesthatgettheircharacteristiccolorfromreddishpigmentsintheircells.

rhizoidsPrimitivestructuresthatnonvascularplantsusetoattachtotheirsubstrate.

Scientific name Theofficialnameforaplant,consistingoftwowords:thegenusandthespecies.

Seed ferns Extinctgroupoffernlikegymnospermsthatproducedseedsatthetipsoftheirleaves.

Seedless vascular plants Agroupofplantsthatincludesferns,horsetails,andclubmossesthathavevasculartissue,butreproducebyspores.

Seeds Fertilizedplantovulesconsistingofanembryoanditsfoodsource.

Sepals Leaflikeoutermoststructuresofaflower.

Seta Stalkthatsupportsthecapsuleinthemosssporophyte.

Sexual reproduction Theformationofoffspringbycombiningeggandsperm.

Shrub Awoodyplantthatproducesseveralstemsandisshorterthatatree.

Sori Theclustersofsporangiaontheleafsurfaceofafern.

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Spadix Aspecialtypeofinflorescencefoundinsomeangiosperms.

Species Aparticulartypeoforganismthatcanbedifferentiatedfromothertypesoforganisms;allmembersofaspecieshavetheabilitytointer-breedandshareacommonevolutionaryhistory.

Sporangium Aspore-producingstructure.

Spores Single-celledreproductivestructuresinbryophytesandseedlessvascularplantsthatarecapableofdevelopingintoaplant.

Spore mother cells Cellsinaplant’sreproductivetissuethatundergomeiosistoformhaploidspores.

Sporophylls Modifiedleavesthatbearsporangia.

Sporophyte Thediploid,spore-producingstageinthealternationofgenerations.

Stamens Themalepartsofflowers,composedofantherandfilament,thatproducepollen.

Sterile jacket Alayerofcellsthatsurroundsthegamete-producingarche-goniumandantheridium.

Sterile whorls Thepartsofaflower(sepalsandpetals)thatdonotpro-ducegametes.

Stigma Thereceptivepotionofthecarpeluponwhichpollengrainsgerminate.

Stipe Thestemofabrownalgaebody.

Stomata Openingsintheleafsurfacethatallowaplanttotakeinandreleasegasses.

Strobilus (plural: strobili) Acone-likeclusterofspore-bearingleaves.

Style Thecarpeltissuethatconnectsthestigmatotheovary;pollentubesgrowthroughthestyletoreachtheovary.

Succession Aseriesofpredictable,cumulativechangesinthecompositionandcharacteristicsofaplantcommunityfollowingdisturbance.

Symbiotic Arelationshipinwhichbothindividualsbenefitfromtheinter-actionandareharmedwhentheyarenottogether.

Synergids Twocellslocatedneartheegginthefemalegametophyteofangiosperms.

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Systematics Thestudyofevolutionaryrelationshipsanddiversity.

taxon Agroupoforganismsatanyhierarchicallevel,suchaskingdomorspecies.

taxonomy Thescienceofclassifyingorganisms.

tepal Sepalsandpetalsthatcannotbedistinguishedfromoneanother.

thallus Asimplevegetativebody,undifferentiatedintoroot,stem,orleaf.

three-merous Havingthreesepals,threepetals,threeorsixstamens,andapistilwiththreecarpels.

tracheids Elongated,thick-walledxylemcellsfoundinmostvascularplantsthatconductandsupport.

tracheophytes Anothernameforvascularplants.

tree Awoodyplantwithasingletrunk.

tube cell Thecellthatdevelopsintothepollentubeinthemalegameto-phytesofseedplants.

Vascular bundles Strandsoftissuethatcontainxylemandphloem.

Vascular cambium Alocalizedareaofcelldivisionandgrowthinplantsthatproducesnewvasculartissueandcontributestoincreaseddiameterofwoodystems.

Vascular tissue Tissueusedtotransportwaterandmineralsthroughouttheplantbody.

Vegetative reproductionAsexualreproductionthroughthebreakingoffofapartoftheplantbodytoproduceanewplant.

Whorl Anarrangementofthreeormorefloralpartsorleavesinacircle.

Xylem Tissuethattransportswaterandmineralsthroughoutthevascularplantbody

Zygospore Adormantsporeformedinzygomycetesandsomealgae.

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129

Abominablemystery,96Adanson,Michel,23Adder’stongueferns,71AgeofHerbals,20–21Airpollution,49Algae

brown,46–47evolutionand,12,34,45,46,52green,12,44–46lichensand,47–48withmossinname,59mutualisticrelationshipwithfungi,

45red,46,47studyof,44valueof,34

Allergies,34,89Amborellaceae,109–110Amentiferae,109Anatomy,29,35–36AngiospermPhylogenyGroup,26Angiosperms

dominantgenerationin,15evolutionof,29,109–111featuresof,96–99firstappearanceof,96lifecycleof,98,100–101,111majorgroupsof,101–105withmossinname,59relationshiptognetophytesof,91symbolismofspecific,96valueof,105–109,110–111

AnimaliaKingdom,12mutualisticrelationshipwithalgae,45relationshipoffungito,12

Antheridiaofbryophytes,54,56,57,58ofseedlessvascularplants,67,68

Araucariaceae,87Arbuscularmycorrhizalfungi,37,39,

40–41ArchaeaKingdom,12Archaeopteris,91

Archegoniaofbryophytes,54,56,57,58ofgymnosperms,85ofseedlessvascularplants,67

Artificialclassificationsystem,23Arums,101Ascomycota,37,39,41–42,47–48Asexualreproduction,36,40,57,76Asteraceae,107Autotrophs,13

BacteriaKingdom,12,106Basalangiosperms,102,109–110Basidiomycota,37,39,42–43,47Beans,105–106Bennettitales,92Binomialnomenclature,7–8,23Bock,Hieronymus,21Brackenferns,73Bracts,91Breadmold,40Bristleconepines,84Brown,Robert,81Brownalgae,46–47Brunfels,Otto,21Bryophytes

ancestorsof,52dominantgenerationin,15evolutionof,29,60–61featuresof,52,54lifecycleof,54,56,66,67–68majorgroupsof,52,54,56–59sporophytesof,66valueof,61

Burns,Robert,96

Calamites,70–71,92Carotenoids,13Carrageenan,34Cellwalls,13

cuticlesand,52offungi,35ofseedlessvascularplants,65–66

130

Charophytes,45–46Cheng Lei Pen Ts’ao(TheMaterials

ofMedicineArrangedAccordingtoPattern,TangShen-wei),20

Chestnutblight,41Chi’enNung(emperorofancient

China),20China,ancient,20Chitin,35Chlorophylls,13Chlorophytes,45Chloroplasts,13Chytrids,37,39,40Cibo,Gherhards,22Clades

ofangiosperms,103–104ofbryophytes,57classificationand,27ofseedlessvascularplants,64,76

Cladistics,26–29Classification,10–11,22–23,25–26,29Clubfungi,37,39,42–43Clubmosses,69–70,77Coal,64Conescales,82,85Cones

ofclubmosses,70ofcycadeoids,92ofcycads,87ofginkgos,88,89ofgnetophytes,91ofgymnosperms,82ofpines,84,85ofWelwitschia mirabilis,80

Conifers,85–87Cordaites,92Coreangiosperms,102–104Corms,70Cotyledons,101–102Croziers,72Crutoselichens,49Cupressaceae,86–87Cuticles,52

Cyanobacteria,47–48,73Cycadeoids,92Cycads(Cycadophyta),87,92

Darwin,Charles,25,26,96Dawnredwoods,89DeJussieu,AntoineLaurent,23,25De Materia Medica(TheMaterialof

Medicine,Dioscorides),20Deciduoustrees,84Decomposers,36,40,43Dendrograms,11,27Dichotomouskeys,29Dicots,101–104Dikaryoticcells,36–37Dioscorides,20,23Diversity

ofangiosperms,96–97valueof,4,6

DoctrineofSignatures,57Doublefertilization,101

Eberspapyrus,20Ecologicalsystems

algaeand,34,44decomposersand,36,40,43functioningof,6successionof,61

Egypt,ancient,20Endosperm,101,111Energyconversion.SeephotosynthesisEngler,109Ephedras,89Epiphytes,109Equisetales,70–71Ethnobotany,6Eudicots,104–105,107,109,110Eukaryoticorganisms,12Evergreens,84Evolution

algaeand,12,34,45,46,52ofangiosperms,29,109–111ofbryophytes,29,60–61

131

cladisticsand,26–29Darwiniantheoryof,25,26offungi,34,39,40geologicaltimescaleofplants,60ginkgosand,88ofgymnosperms,29,91–92heterosporyand,68ofroots,69ofseedlessvascularplants,29,64,

66,76ofseedsandpollen,82stomataand,58Seealsophylogeny

Fabaceae,105–106Families,9,10Ferns,70–74,76Fiddleheads,72,73,77Fieldguides,29Filicales,73–74,76Five-merousflowers,105Flagella,40Flavonoids,46Floras,29Floweringplants.SeeangiospermsFolioselichens,49Food

algaeas,34angiospermsas,105–107,109,

110–111fungias,42gymnospermsas,93seedlessvascularplantsas,77

Four-merousflowers,105Fronds,66,73Fruits,110–111Fruticoselichens,49Fuchs,Leonart,21Fungi

anatomyof,35–36dangersof,34,42–43evolutionof,34,39,40lichensand,47–48

lifecycleof,36–37,40,41–42majorgroupsof,37,39–43membersof,12mutualisticrelationshipwithalgae,

45valueof,34,36,42

Gametes,14,15,98Gametophytes

ofangiosperms,100ofbryophytes,54,56,57,59,67–68described,15ofgymnosperms,84ofseedlessvascularplants,66,67–68

Gemmae,57Generations,alternate,15,54,66Genusnames,8,10,23Ghini,Luca,21–22Giantrafflesia,110Giantsequoias,84Ginkgos,87–89,92Glomeromycota,37,39,40–41Gnetophytes,89,91Granitemosses,59Grasses,107Greece,ancient,20Greenalgae,12,44–46Gymnosperms

evolutionof,29,91–92featuresof,82,84lifecycleof,82,84–85majorgroupsof,82,85–89,91seedsof,80–81valueof,87,93

Hallucinogens,43Herbalmedicines,6,57Herbaria,22Herbariumsheets,22Herbs,107Heterospory,68Heterotrophs,12,36

Seealsofungi

132

Historia Naturalis(NaturalHistory,PlinytheElder),20

Historia Plantarum(HistoryofPlants,Theophrastus),20

Homeopathicmedicine,57Homospory,67–68,73Honeymushrooms,36Hornworts,58,61Horsetails,70–71Hunter-gatherers,4Hydroids,59Hyphae,35–36Hypotheses,93

Identificationguides,29Illiciales,109–110Inflorescences,98–99,110InternationalBotanicalCongresses,

9–10InternationalCodeofBotanical

Nomenclature(ICBN),8–10,11Iridaceae,108–109Isotales,70

Kaempfer,Engelbert,89Kelp,47Kingdoms

definitionof,10different,11–13

Landscaping,93“TheLanguageofFlowers,”96Latin,8Leaves

cotyledonsofangiosperms,101–102evolutionof,66oflycophytes,68ofmarattoidferns,71–72ofmonilophytes,70ofophioglossoidferns,71ofseedlessvascularplants,69ofwaterferns,73ofWelwitschia mirabilis,80

Legumes,105–106Lepidodendrontrees,64Leptoids,59Lichens,47–49,59Lifecycles

alternationofgenerations,15ofangiosperms,98,100–101,111ofbryophytes,54,56,66,67–68offungi,36–37,40,41–42ofgreenalgae,44–45ofgymnosperms,82,84–85lengthof,4ofseedlessvascularplants,66,67–68

Liliaceae,108,109Liliopsida,101,104–105Linnaeus,Carolus,7–8,23Liverworts,57,60–61Lycophytes,64,68–70,92

Magnol,Pierre,22,23Magnoliaceae,109Magnoliids,103–104,110Magnoliopsida,101–104Marattoidferns,71–72Marsileales,73The Material of Medicine(Dioscorides),

20The Materials of Medicine Arranged

According to Pattern(TangShen-wei),20

MedicineDoctrineofSignaturesand,57fungias,34,42gymnospermsas,89herbal,6,57mossesas,61prescriptiondrugs,6

Megaphylls,70Megaspores,68Meiosis

ofchytrids,40ofclubfungi,42described,15

133

ofgreenalgae,45ofgymnosperms,84–85ofsacfungi,42

Microspores,68Mitosis,15,85Modernclassificationsystem,26Molds,34Monilophytes,64,70–74,76Monkeypuzzletrees,87Monocots,101,104–105,107,108,110Monophyleticgroups,27,89Morphology,29Mosses,56,58–59,61Mushrooms,42–43Mutualism,41,45,47–48Myceliaoffungi,35–37,41–42Mycorrhizae,41Mycorrhizalfungi,69

Nakedseedplants.SeegymnospermsNames/naming.SeetaxonomyNamibDesert,80Narcotics,107Naturalclassificationsystem,25Natural History(PlinytheElder),20Naturalselection,25Navalstores,93Nonfloweringseedplants.See

gymnospermsNorfolkIslandpines,87Nuclei,12,36–37Nymphaeaceae,109–110

Ophioglossoidferns(ophioglossales),71

Orchidaceae,109Orchids,101Orders,11Organelles,12The Origin of Species(Darwin),25Ornamentation,87,93,105,107,

108–109Ovules

ofangiosperms,97–98,100ofgymnosperms,85

Paleobotanists,89Parasiticplants,13Peatmosses,59,61Penicillin,34,42Petals,roleof,98Pharmaceuticalindustry,6Phloem,82,84Photoautotrophs,13Photosynthesis

described,13redalgaeand,47sporophytesofhornworts,58valueof,6

Phycobilins,47Phycology,44Phylocode,31Phylogeny,10,26–29,93

SeealsoevolutionPigments,46,47

SeealsophotosynthesisPinaceae,85–86Pines,84–86,93PlantaeKingdom,13Plants,definingtraitsof,13–14PlinytheElder,20Podocarpaceae,87Poisons,34,42–43,107Pollen

ofangiosperms,98,100,101,104,110–111

evolutionof,82ofgymnosperms,85,87,88,91

Polynomialnomenclature,7,22–23Prantl,109Prasinophytes,45Prescriptiondrugs,6Printingpress,20–21Prokaryoticorganisms,12ProtistaKingdom,12Protists,37,47

134

Protogymnosperms,91Protonemas,54,56Psilotales,70–71Puffballs,42

Quillworts,70

Ranunculaceae,109Ray,John,22,101Redalgae,46,47Redtides,47Redwoodtrees,84Religiousceremonies,4,43Reproduction.SeelifecyclesRespiratoryillnesses,34,89Resurrectionplants,69Rhizoids,54,56Rome,ancient,20Roots,66,69,70Rosaceae,105Roses,105Rusts,43

Sacfungi,37,39,41–42Salviniales,73Seedferns,91,92Seedlessnonvascularplants.See

BryophytesSeedlessvascularplants

evolutionof,29,64,66,76featuresof,65–66lifecycleof,66,67–68majorgroupsof,64–65,68–74,76withmossinname,59valueof,76–77

Seedsofangiosperms,98,101evolutionof,82naked,80–81valueof,82

Sepals,98Seta,59Sexualreproduction,40,41–42,44–45,

56Shelffungi,43Sloths,45Smuts,43Sori,74Spadixes,110Species

abbreviationsfor,11ofalgae,45,46,47ofangiosperms,96,109ofbryophytes,52,56,57,58,59definitionof,10–11offungi,37,40ofgymnosperms,82,85,86,87,89identifyingname,8inPlantaeKingdom,13ofseedlessvascularplants,68,69,70,

71,73Species Plantarum(Linnaeus),23Sphagnummoss,61Spikemosses,69Sporangia

ofgymnosperms,84ofseedlessvascularplants,66,67,

68–69,70–71,73–74Spores

asexualreproductionof,36,40,57ofgymnosperms,84–85ofseedlessvascularplants,67sexualreproductionof,40,41–42,

44–45,56Sporophylls,68–69,70Sporophytes

ofangiosperms,100,101ofbryophytes,54,56,57,58,59described,15ofgymnosperms,84ofseedlessvascularplants,66,67,69

Sterilejackets,14Stomataofhornworts,58Stoneworts,46Strobili,70,80Sunflowers,107

135

Symbioticrelationships,34,69,106Systematics

classification,10–11dataused,29,31early,22–23,25hypothesesin,93phylogeny,10taxonomy,7–11,31,57

TangShen-wei,20Taxa,11Taxonomy

abbreviationsand,11binomialsystem,7–8commonplantnames,7DoctrineofSignaturesand,57ICBNrules,8–10,11levelsof,10Phylocodesystem,31

Tepals,98Thallus,57,58Theophrastus,20Theory,described,26

Three-merousflowers,105Toadstools,42Tracheids,65Tracheophytes,65TreeofLifeProject,26Trees,64,84,105Tribalpeoples,6Trimeniaceae,109–110Trueferns,73–74,76Truemosses,59

Vascularplants,65Vegetativereproduction,57

Waterferns,73Welwitschia mirabilis,80,89Whiskferns,70–71Whorlsofflowers,98,105

Xylem,82,84

Zygomycetes,37,39,40Zygospores,40

136

J. Phil Gibson holds degrees in botany from Oklahoma State University(B.S.)andtheUniversityofGeorgia(M.S.),andaPh.D. inenvironmen-tal population and organismic biology from the University of Colorado.He is currently an associate professor in the Department of Botanyand Microbiology and the Department of Zoology at the University ofOklahoma. His research investigates the ecology and evolution of plantreproductivesystems.Healsoconductsconservation-focusedresearchontreespecies.Hehaspublishedavarietyofresearchpapersandpresentedhis work at scientific conferences. Gibson is a member of the ProjectKaleidoscopeFacultyforthe21stCenturyinrecognitionofhiseffortstoimprove undergraduate science education. He is also an active memberof theBotanicalSocietyofAmericaandtheAssociationofSoutheasternBiologists.

terri r. Gibsonholdsabachelor’sdegreeinzoologyfromtheUniversityofGeorgia.Shehasworkedasascientificillustratorandalsoasaresearchassistant studying, among other things, plant population genetics, plantmorphology,andhumanimmunodeficiencyvirus(HIV).Sheiscurrentlypursuingacareerinchildren’sliterature.

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