Chapters 29 & 30:

Plant DiversityAP Biology 2013

Colonization of the LandSince colonizing land, plants have diversified into about 290,000 speciesEvolved from green algae

Charophyceans are closest relatives of land plants and share these characteristics:

Rose-shaped complexes for cellulose synthesis Peroxisome enzymeStructure of flagellated spermFormation of phragmoplast (aids in cell plate formation)

Plants have been on land for at least 475 million years

1 µm

Chara species, a pond organism

Coleochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM)

40 µm

5 mm

Fig. 29.3

1 µm

Origin of land plants (about 475 mya)

Origin of vascular plants (about 425 mya)

Origin of extant seed plants (about 305 mya)

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1

3

2

1 ANCESTRAL GREEN ALGA

500 450 400 350 300 50 0 Millions of years ago (mya)

Liverworts

Mosses

Hornworts

Lycophytes (club mosses, spike mosses, quillworts) Pterophytes (ferns, horsetails, whisk ferns)

Gymnosperms

Angiosperms

Land plants Vascular plants

Nonvascular

plants (bryophytes)

Seedless vascular plants

Seed plants

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Fig. 29.7

Derived AdaptationsSo closely related to green algae that some think they should be included as plantsPlants differ from charophyceans in five key ways:

Apical meristemsAlteration of generationsWalled spores produced in sporangiaMulticellular gametangiaMulticellular dependent embryos

1 µm

Red algae

Chlorophytes

Charophytes

Embryophytes

ANCESTRAL ALGA

Viridiplantae S

treptophyta

Plantae

Fig. 29.4

1 µm

Gamete from another plant

Key Haploid (n) Diploid (2n)

Gametophyte (n)

Mitosis Mitosis

Spore Gamete

MEIOSIS FERTILIZATION

Zygote

Mitosis Sporophyte (2n)

Alternation of generations

2n

n n n

n

Fig. 29.5

1

2

3

Important Plant TerminologySporophyte produces spores in organs called sporangia

Diploid cells called sporocytes undergo meiosis to generate haploid spores

Gametes are produced within organs called gametangia

Female gametangia are called archegonia (produce eggs and are site of fertilization)Male gametangia are called antheridia (produce and release sprem)

1 µm

Spores Sporangium

Longitudinal section of Sphagnum sporangium (LM)

Sporophyte

Gametophyte

Sporophytes and sporangia of Sphagnum (a moss)

Fig. 29.5

1 µm

Female gametophyte

Male gametophyte

Archegonia, each with an egg (yellow)

Antheridia (brown), containing sperm

Archegonia and antheridia of Marchantia (a liverwort)

Fig. 29.5

Important Plant TerminologyApical Meristems - where plants exhibit continual growth

Cells here can differentiate into various tissues

Cuticle - waxy coating of the epidermis Mycorrhizae - symbiotic association between plants and fungi that helps plants obtain nutrients Plants are grouped based on presence of vascular tissue

1 µm

Apical meristem of shoot

Developing leaves

Shoot 100 µm 100 µm Root

Apical meristem of root

Apical meristems of plant roots and shoots

Fig. 29.5

Seed - an embryo surrounded by a protective coat

Seed plants form a clade that can be divided into the clades gymnosperm and angiosperm

BryophytesNonvascular plantsRepresented by three phyla of small herbaceous (nonwoody) plants

Liverworts - phylum HepatophytaHornworts - phylum AnthocerophytaMosses - phylum Bryophyta

Sequence of bryophyte evolution is not clear, but mosses are most closely related to vascular plantsIn all three phyla, gametophytes are larger and longer-living than sporophytes

Nonvascular plants (bryophytes)

Seedless vascular plants Gymnosperms Angiosperms

Protonemata (n)

Key Haploid (n) Diploid (2n)

“Bud”

“Bud”

Male gametophyte (n)

Antheridia Sperm

Egg

Archegonia Gametophore Spores

Spore dispersal

Peristome

Sporangium

Female gametophyte (n) Rhizoid

FERTILIZATION (within archegonium) Zygote

(2n)

Archegonium

Embryo

Seta Capsule (sporangium) Foot

Young sporophyte (2n)

MEIOSIS Mature sporophytes

2 m

m

Capsule with peristome (LM) Female

gametophytes

1 µm

Fig. 29.8

1 µm

An Anthoceros hornwort species

Sporophyte

Gametophyte 1 µm

Polytrichum commune, hairy-cap moss

Capsule

Seta

Sporophyte (a sturdy plant that takes months to grow)

Gametophyte

Fig. 29.9

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5

6

Importance of MossesCapable of inhabiting diverse and extreme environments (although most common in moist forests and wetlands)Help retain nitrogen in soilSphagnum (peat moss) forms deposits of partially decayed organic material called peat which can be used for fuel

Reservoir for organic carbonOverharvesting or water level drop could cause stored CO2 to be released into the atmosphere

1 µm With moss Without moss

RESULTS

Ann

ual n

itrog

en lo

ss

(kg/

ha)

6

5

4

3

2

1

0

Fig. 29.10

1 µm

Peat being harvested from a peatland

(a) “Tollund Man,” a bog mummy dating from 405–100 B.C.E.

(b)

Fig. 29.11

Seedless Vascular PlantsDate back to 420 million years agoVascular tissue allowed the plants to grow tallHave flagellated sperm (require moist environments)Early tiny plants had independent, branching sporophytes but lacked the other derived traits of vascular plantsSporophytes are the larger generation; gametophytes are tiny plants that grown on or below the soil surface

Nonvascular plants (bryophytes)

Seedless vascular plants Gymnosperms Angiosperms

1 µm

Key

Haploid (n) Diploid (2n)

MEIOSIS Spore dispersal

Spore (n)

Young gametophyte

Rhizoid

Underside of mature gametophyte (n)

Antheridium

Sperm

Archegonium Egg

FERTILIZATION Zygote (2n)

Gametophyte

New sporophyte

Mature sporophyte (2n)

Fiddlehead (young leaf)

Sporangium

Sorus

Sporangium

Fig. 29.13

Evolution of LeavesLeaves - organs that increase surface area of vascular plants (capture more solar energy)Two types:

Microphylls - with a single vein (perhaps evolved from outgrowths of stems)Megaphylls - highly branched vascular system (perhaps evolved from webbing of flattened branches)

Sporophylls - modified leaves with sporangia

Most seedless vascular plants are homosporous. Seed plants and some seedless vascular plants are heterosporous

1 µm

Vascular tissue Sporangia Microphyll

(a) Microphylls

1 µm (b) Megaphylls

Overtopping growth

Megaphyll

Other stems become reduced and flattened.

Webbing develops.

Fig. 29.14

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8

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Seedless Vascular Plant PhylaLycophyta - club mosses, spike mosses, and quillworts

Small herbaceous plantsPterophyta - ferns, horsetails, and whisk ferns

Ferns - most diverse group

These phyla formed the first forests during the Carboniferous period

Caused major global coolingEventually became coal

1 µm

Selaginella moellendorffii, a spike moss

Isoetes gunnii, a quillwort

Diphasiastrum tristachyum, a club moss

Strobili (clusters of sporophylls)

2.5 cm

1 cm

1 µm

Athyrium filix-femina, lady fern

Equisetum arvense, field horsetail

Vegetative stem

Strobilus on fertile stem

Psilotum nudum, a whisk fern

4 cm

25 c

m

1.5

cm

Fig. 29.15

Seeds Bearing PlantsChanged the course of plant evolutionPlants could become dormant Reduced gametophytes are protected in ovules and pollen grains

Develop within the walls of spores and retained within the tissue of the parent sporophyte

HeterosporyOvules and Pollen

PLANT GROUP

Mosses and other nonvascular plants

Gametophyte

Sporophyte

Sporophyte (2n)

Gametophyte (n)

Dominant

Reduced, dependent on gametophyte for nutrition Dominant

Reduced, independent (photosynthetic and free-living)

Ferns and other seedless vascular plants

Dominant

Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition

Seed plants (gymnosperms and angiosperms)

Angiosperm Gymnosperm

Microscopic female gametophytes (n) inside these parts of flowers

Microscopic female gametophytes (n) inside ovulate cone

Microscopic male gametophytes (n) inside these parts of flowers

Microscopic male gametophytes (n) inside pollen cone

Sporophyte (2n) Sporophyte (2n)

Sporophyte (2n)

Gametophyte (n)

Example

Fig. 30.2

HeterosporySeed plants evolved from plants that had megasporangia (produce megaspores that give rise to female gametophytes)

Ovule consists of a megasporangium, megaspore, and protective integumentsSeed plants evolved from plants that had microsporangia (produce microspores that give rise to male gametophytes - contained in pollen)

Pollen grain germination involves pollen tube that discharges two sperm into the female gametophyte within the ovule

Pollination - transfer of pollen to the part of the seed plant that contains the ovules

Seed develops from the whole ovule

Sporophyte embryo along with its food

supply packaged in a protective coat

Immature ovulate cone

Integument (2n)

Spore wall

Megaspore (n)

Female gametophyte (n)

Egg nucleus (n)

Discharged sperm nucleus (n)

Pollen tube Male gametophyte (n)

(a) Unfertilized ovule

Megasporangium (2n)

Pollen grain (n) Micropyle

(b) Fertilized ovule (c) Gymnosperm seed

Seed coat

Spore wall

Food supply (n)

Embryo (2n)

Fig. 30.3

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Gymnosperms

ConifersInclude four plant phyla: Cycadophyta, Gingkophyta, Gnetophya, ConiferophytaAppear early in the fossil record

Nonvascular plants (bryophytes)

Seedless vascular plants Gymnosperms Angiosperms

Cycas revoluta

Ginkgo biloba leaves and fleshy seeds

Ginkgo biloba pollen-producing tree

Fig. 30.5

Douglas fir

Common juniper

European larch

Sequoia

Wollemi pine Bristlecone pine

Ovulate cones Gnetum

Ephedra

Welwitschia

Gymnosperm Life CycleKey features:

Dominance of sporophyte generationDevelopment of seeds from fertilized ovulesRole of pollen in transferring sperm to ovules

Key Haploid (n) Diploid (2n)

Mature sporophyte (2n)

Ovulate cone

Pollen cone

Microsporocytes (2n)

Microsporangia Microsporangium (2n)

Seedling

Archegonium

Surviving megaspore (n)

MEIOSIS

Megasporangium (2n) Pollen grain Pollen

grains (n) MEIOSIS

Female gametophyte

Megasporocyte (2n)

Integument

Sperm nucleus (n) Egg nucleus (n)

Pollen tube

Seed coat (2n)

FERTILIZATION

Food reserves (n)

Seeds

Embryo (new sporophyte) (2n)

Ovule

Fig. 30.6

AngiospermsFlowering plantsSeed plants that produce reproductive structures called flowers and fruits

Key adaptation of angiospermsFlower is a specialized structure for sexual reproduction

Most widespread and diverse of all plants

Nonvascular plants (bryophytes)

Seedless vascular plants Gymnosperms Angiosperms

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Flower and FruitsSpecialized shoot with modified leaves

Sepals enclose the flowerPetals brightly colored to attract pollinators Stamens which produce pollenCarpels which produce ovules

Fruits consist of a mature ovary and can be dispersed by wind, water, or animals

Figs. 30.7-30.9

Stamen Anther

Filament

Stigma Carpel

Style

Ovary

Petal

Sepal

Ovule Tomato Ruby grapefruit

Hazelnut

Nectarine

Milkweed Wings

Seeds within berries

Barbs

Angiosperm Life CycleDouble fertilization occurs when a pollen tube discharges two sperm into the female gametophyte within an ovuleOne sperm fertilizes the egg ; the other combines with two nuclei in the center cell of the female gametophyte and initiates development of a food-storing endospermEndosperm nourishes the developing embryo

Fig. 30.10

Anther Mature flower on sporophyte plant (2n)

Germinating seed

Megasporangium (2n)

Ovary

Embryo (2n)

Endosperm (3n) Seed coat (2n)

Seed

Antipodal cells Central cell Synergids

Female gametophyte (embryo sac)

Egg (n)

Egg nucleus (n)

Surviving megaspore (n)

Pollen tube

Sperm (n)

Style

Sperm Pollen tube

Stigma

Pollen grains

Tube cell Generative cell

Microspore (n)

Male gametophyte (in pollen grain) (n)

Ovule (2n)

MEIOSIS

MEIOSIS

Discharged sperm nuclei (n)

FERTILIZATION Zygote (2n)

Microsporangium Microsporocytes (2n)

Nucleus of developing endosperm (3n)

Key Haploid (n) Diploid (2n)

Angiosperm EvolutionOriginated at least 140 million years agoPrimitive fossils of 125 million-year-old angiosperms display both derived and primitive characteristicsThought that ancestors had separate pollen producing and ovule producing structures before they were combined into a single flower

Fig. 30.11

(a) Archaefructus sinensis, a 125- million-year-old fossil

(b) Artist’s reconstruction of Archaefructus sinensis

Carpel

Stamen

5 cm

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Angiosperm DiversityTwo groups:

Monocots - one cotyledon Eudicots - two cotyledons

Basal angiosperms - less derived Magnoliids - share some traits with basal angiosperms but are more closely related to monocots and eudicots

Water lily

Star anise

Amborella trichopoda

Basal Angiosperms

Fig. 30.13

Orchid Monocots

Lily

Pygmy date palm

Anther

Filament

Stigma Ovary

Barley, a grass

California poppy Dog rose

Pyrenean oak

Snow pea Zucchini

Eudicots

Angiosperm DiversityMonocot

Characteristics Eudicot

Characteristics

Embryos

One cotyledon Two cotyledons

Leaf venation

Veins usually parallel

Veins usually netlike

Stems

Vascular tissue scattered

Vascular tissue usually arranged

in ring

Roots

Root system usually fibrous (no main root)

Taproot (main root) usually present

Pollen

Pollen grain with one opening

Pollen grain with three openings

Flowers

Floral organs usually in

multiples of three

Floral organs usually in multiples

of four or five

Monocot Characteristics

Eudicot Characteristics

Fig. 30.13

Links Between Angiosperms and AnimalsPollination of flowers by animals and transport of seeds by animals Crucial for survival of humans

Food, wood, and medicinesHumans are destroying habitats and causing extinction

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