The Evolution of Seed Plantswtyler-irsc.weebly.com/uploads/1/9/8/6/19866611/ch29_lecture-spr11.pdf · 29 The Evolution of Seed Plants ... Gymnosperms? •29.3 What ... Success of

The Evolution of

Seed Plants

29

29 The Evolution of Seed Plants

• 29.1 How Did Seed Plants Become

Today’s Dominant Vegetation?

• 29.2 What Are the Major Groups of

Gymnosperms?

• 29.3 What Features Contributed to the

Success of the Angiosperms?

• 29.4 How Do Plants Support Our

World?

29.1 How Did Seed Plants Become Today’s Dominant

Vegetation?

Late in Devonian, some

plants developed

secondary growth

Thickened woody

stems of xylem

The first species with

secondary growth were

progymnosperms

seedless vascular

plants, now extinct

http://www.futura-sciences.com/uploads/tx_oxcsfutura/comprendre/d/images/600/fig_1213.jpg


Vegetation?

Earliest seed plants from Devonian

These seed ferns were also woody

Clades of seed ferns are known only

as fossils

Two of the clades are basal to

surviving seed plants

http://www.palaeos.com/Plants/Lists/Glossary/Images/SeedFern.jpg

Figure 29.1 The Fossil Record of Seed Plants and Some of Their

Extinct Seedless Relatives


Vegetation?

Surviving seed plants fall into two groups:

Gymnosperms: conifers and cycads

Angiosperms: flowering plants

Figure 29.2 The Major Groups of Living Seed Plants


Vegetation?

Gametophyte generation is reduced even

further than it is in ferns

Haploid gametophyte develops partly or

entirely attached to sporophyte

Nonvascular

– Mosses

Vascular,

seedless – Ferns

Vascular, seed plants

Figure 29.3 The Relationship between Sporophyte and

Gametophyte (Part 1)

Figure 29.3 The Relationship between Sporophyte and

Gametophyte (Part 2)


Vegetation?

Only earliest gymnosperms had swimming

sperm

Without swimming sperm, seed plants

were independent of water for sexual

reproduction

Major advantage for terrestrial lifestyle

http://www1.fccj.cc.fl.us/dbyres/pollen400_small1.jpg

Pine pollen germinating

to produce a pollen tube

that will carry the male

gamete to the egg.


Vegetation?

Seed plants are heterosporous

Produce two types of spores

One becomes female gametophyte, one

becomes male gametophyte

Seed plants form separate megasporangia

and microsporangia

http://bio1151.nicerweb.com/doc/c

lass/bio1151/Locked/media/ch30/

30_03OvuleToSeedA.jpg

The Seed Plants

Megaspores develop into female

(mega-)gametophytes

Retained within megasporangia

and dependent on sporophyte

Only one of the meiotic products

in megasporangium survives

Surviving haploid nucleus

produces a multicellular female

(mega-)gametophyte

Retained within megasporangium,

megagametophyte matures into

egg and is eventually fertilized

next generation (sporophyte)

http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20102/Bio%20102%20lectures/Seed%20Plants

Seed Plant Reproduction

Sporophyte

MeiosisFertilization

Seed

MegasporesMicrospores

Megagametophyte

Microgametophyte(pollen grain)

Sperm Eggs

ZygoteDiploid (2n)

Haploid (1n)

(inside megasporangium)

MegasporangiaMicrosporangia

Contained in

parent sporophyte

The Seed Plants

Retained within

megasporangium, the

megagametophyte

develops into an egg

that is eventually

fertilized next

generation

(sporophyte)

http://herbarium.usu.edu/teaching/4420/seed.GIF


Vegetation?

Megasporangium is surrounded by integument made of sporophytic (2n) structures

Megasporangium and the integument together form the ovule, which develops into a seed

http://herbarium.usu.edu/teaching/4420/seed.GIF


Vegetation?

In microsporangium, microspores divide mitotically to produce the male gametophyte, or pollen grain

Walls of pollen grains contain sporopollenin, the most resistant biological compound known protects pollen grain from chemicals and dehydration

Figure 29.4 Pollen Grains


Vegetation?

Pollination

When pollen grain lands near a female gametophyte

Pollen tubesproduced that digests way through sporophyte tissue to megagametophyte

Sperm are released from the tube, and fertilization results in a diploid zygote.

http://pix.botany.org/Setabot/abot-90-5_700.jpg


Vegetation?

Resulting diploid zygote

divides to produce an

embryonic sporophyte

Growth is then

suspended

Embryo enters a

dormant stage, with

the end product being

a multicellular seed

http://nosheteria.com/uploaded_images/PumpkinSeeds.jpg

Pumpkin seeds

Seed Plant Reproduction

Sporophyte

MeiosisFertilization

Seed

MegasporesMicrospores

Megagametophyte

Microgametophyte(pollen grain)

Sperm Eggs

ZygoteDiploid (2n)

Haploid (1n)

(inside megasporangium)

MegasporangiaMicrosporangia

The Seed Plants

Seed contain tissues from three generations

Seed coat (from integument) and megasporangiumdevelop from ovule tissues of diploid sporophyte parent

Within megasporangium is haploid female gametophytetissue (contains nutrients) of next generation

Third generation, the embryo,is the new diploid sporophyteis contained in the center of seed package.

2n

1n

2n

2n


Vegetation?

Seeds are well-protected resting stages.

May remain viable for many years,

germinating when conditions are favorable.

Seed coat protects from drying out as well

as predators.

Many seeds have adaptations for dispersal.

http://winemaking.jackkeller.net/sandburr.jpg

Common sand burr

(Cenchrus echinatus)


Vegetation?

Seeds are one of the main reasons for success of

seed plants — dominant life forms in terrestrial

environments

www.utexas.edu/research/ica/metaponto/meta81www.anselm.edu/homepage/jpitocch/genbios

Dandelion

Secondary growth also

contributes to their success

Wood: proliferated xylem,

gives support and allows

plants to grow above their

competitors for sunlight

In the course of seed plant

evolution, many lost the

woody growth habit; but have

other advantages.

http://cache.eb.com/eb/image?id=72251&rendTypeId=35 http://mayhem-chaos.net/photoblog/images/pine_tree_med.jpg


Vegetation?

29.2 What Are the Major Groups of Gymnosperms?

Extant gymnosperms are probably a clade

Gymnosperm

―naked-seeded‖

ovules and seeds are not protected

by ovary or fruit tissue

http://www.conifers.org/pi/pin/lambertiana5.jpg

Pinus longaeva, Bristlecone

pine, cone and needles

Figure 29.2 The Major Groups of Living Seed Plants

Four major groups of living gymnosperms:

• Cycads: Cycadophyta—140 species

http://www.biologyreference.com/images/biol_02_img0213.jpg



• Ginkgos: Ginkgophyta—one living

species, Ginkgo biloba

Branch of male Ginkgo biloba with

clusters of pollen-producing

microsporophylls

Branch of female Ginkgo biloba

with leaves and ovules



• Gnetophytes: Gnetophyta—90 species in 3 genera

Ephedra viridis (Mormon tea or

joint fir) with cones; Arizona



• Conifers: Coniferophyta—600 species,

the cone bearers

http://www.nasa.gov/centers/goddard/images/content/156030main_Conifers_JPG.jpg


Figure 29.6 Diversity among the Gymnosperms

All living gymnosperms except gnetophytes have only tracheids for water conduction and support

Gymnosperms were dominant during Mesozoic

Tallest gymnosperms are California coastal redwoods — over 100 m

Angiosperms have vessel elements and fibers alongside of tracheids

Tracheids and

fiber tracheids

http://www.uri.edu/cels/bio/plant_anatomy/images/47.gif



Gymnosperms were dominant

during the Mesozoic, until

about 65 Mya.

Today, conifers still dominate

many forests, especially at

high latitudes and altitudes.

The oldest living organism on

Earth is a bristlecone pine

that germinated about 4,800

years ago.

http://media.rd.com/rd/images/rdc/family-travel/poi/CA-poi-

ancient-bristlecone-pine-forest-af.jpg

Male and female cones contain the

reproductive structures of conifers.

Megastrobilus (female, seed-bearing Cone)

Modified stem, bearing a tight cluster of woody

scales (reduced branches)

Produces seeds


Microstrobilus (male, pollen-bearing cone)

―Cone-like‖ structure

Scales are modified leaves; not woody

Microsporangia produces microspores

pollen grains (microgametophyte)


Pine life cycle:

Wind carries pollen grains from microstrobilus to

megastrobilus


The ovule consists of the integument, the

megasporangium inside it, and the tissue

attaching it to the maternal sporophyte

www.umanitoba.ca/Biology/lab8/images

Micropylar

end


The Gymnosperms: Naked Seeds

Pollen grains enter ovule through a small opening in the integument at tip of the ovule called the micropyle

www.botany.hawaii.edu/faculty/webb/BOT201/Conifers

Pollen grains. Note the

swollen bladders

which helps them float

in air currents.


Two sperm travel through pollen tube

One fertilizes egg

One degenerates


Animation 29.1 Life Cycle of a Conifer

Figure 29.8 The Life Cycle of a Pine Tree

Most conifer ovules

are born on the

upper surfaces of

the cone scales

Stone pine cone with pine

nuts - note two nuts (seeds)

that develop from the ovule

under each cone scale



Some pine cone scales (e.g., longleaf and

slash pines) can only be opened by fire

to release the seeds

helps insure new growth after fires.

Some conifers have soft, fleshy, fruit-like tissue

around seeds (e.g., juniper and yew ―berries‖)

Animals may eat these and then disperse

the seeds in their feces.

www.bevlaw.com/imageshttp://botit.botany.wisc.edu/courses/img/bo

t/402/Reference_Images/Taxus_cuspidata

Juniper “berries”

used in gin

Yew “berries”


29.3 What Features Contributed to the Success

of the Angiosperms?

Angiosperms:

―enclosed seed‖

Oldest fossils are Jurassic, 150 my old

Explosive species radiation angiosperms became dominant during Tertiary in only 60 million years

Over 250,000 species exist today

http://gpc.edu/~pgore/myphotos/fossils/angiosperm-leaf.jpg


of the Angiosperms?

Extreme of evolutionary trends in vascular plants:

Sporophyte generation becomes larger,

gametophyte become smaller

Female gametophyte even more reduced —

usually only seven cells

Synapomorphies (shared, derived traits) in angiosperms:

Double fertilization

Triploid endosperm – nutritive tissue in seeds

Ovules and seeds enclosed in a carpel

Flowers

Fruits

Xylem with vessel elements and fibers

Phloem with companion cells

http://www.gallerym.com/images/work/big/schatz_howard_Botanica-%20Orchid%20Phala%20001_L.jpg

Phalaenopsis Orchid


of the Angiosperms?

Double fertilization:

Microgametophyte has two male gametes

One nucleus combines with egg

Second nucleus combines with two haploid nuclei of female gametophyte to form triploid nucleus endosperm (3n)

Endosperm nourishes developing sporophyte

http://www.lclark.edu/~seavey/images%20/carpel.jpg


of the Angiosperms?

Angiosperm (―enclosed seed‖)

Ovules and seeds are enclosed in a modified leaf called a carpel

Carpels provide protection

May interact with pollen to prevent self-pollination

Angiosperms also produce flowers and fruits


of the Angiosperms?

Xylem contains vessel elements

specialized for water transport

Figure 7. Longitudinal section of the stem showing

primary and secondary xylem.

Figure 8. Detail of Fig. 7 showing vessel element

with oblique perforation plate (pp) and scalariform

pitting (sp) pattern.

Figure 9. Detail of Fig. 7 showing helically thickened

walls (ht) of the smaller vessel elements, probably of

metaxylem and xylem parenchyma (pa).

http://lifesciences.asu.edu/plb306/t3.JPG


of the Angiosperms?

Fiber cells: important in supporting plant

body

http://student.nu.ac.th/u46410387/fiber.jpeg


of the Angiosperms?

Phloem contains

companion cells

Woody angiosperms

show secondary

growth, producing

secondary xylem and

phloem and growing

in diameter

http://www.botany.hawaii.edu/faculty/webb/Bot201/CellTissOrgan/201LabTypVascPlantTheme.htm


of the Angiosperms?

Flowers

Stamens bear

microsporangia

consist of filament

and anther


of the Angiosperms?

Flowers

Carpels bear

megasporangia

One or more

carpels form the

pistil — stigma,

style, ovary and

ovule

In this example, the

pistil is a single carpel


of the Angiosperms?

Flowers often have other specialized leaves that often play a role in attracting pollinators

Petals – inner whorl (collectively, the corolla)

Sepals – outer whorl (collectively, the calyx)

Calyx protects immature flower in bud before it opens


of the Angiosperms?

Figure 29.5 Pollination in an Angiosperm (Part 1)

Figure 29.5 Pollination in an Angiosperm (Part 2)

Types of flowers:

Perfect flowers

have both mega-

and microsporangia

http://leon.ifas.ufl.edu/images

Easter lily


of the Angiosperms?

Imperfect flowers

either mega or microsporangia, but not both

Begonia carpellate

(female) flower

Begonia stamenate (male) flower

www.botany.hawaii.edu/faculty/webb/BOT410/


of the Angiosperms?

Monoecious: ―one-housed‖

male and female flowers occur on the same plant or in perfect flowers

Dioecious: ―two-housed‖

male and female flowers on different plants

separate sexes

www.botany.hawaii.edu/faculty/webb/BOT410/Angiosperm

Dioecious squash

female and male

flowers

http://www.sidthomas.net/images/maize400.JPG


of the Angiosperms?

If petals and sepals are indistinguishable, they are called tepals

Inflorescence: grouping of flowers

different families have characteristic types

Magnolia flower with tepals

www.life.uiuc.edu/plantbio/digitalflowers/picts/Asclepiadaceae

Asclepias curassavica

from tropical America

http://encyclopedia.laborlawtalk.com/wiki/images


of the Angiosperms?

Figure 29.10 Inflorescences

Flowers of basal clades have many tepals, carpels, and stamens

Evolutionary trend toward

reduction in numbers of floral organs,

changes in symmetry, and…

fusion of parts

Basal group – magnolias

Higher group – orchids


of the Angiosperms?

Figure 29.11 Flower Form and Evolution

Carpels and stamens

may have evolved

from modified leaves

Carpels became

progressively more

fused and buried in

the receptacle tissue,

forming the ovary


of the Angiosperms?

Figure 29.12 Carpels and Stamens Evolved from Leaflike

Structures (Part 1)

Figure 29.12 Carpels and Stamens Evolved from Leaflike

Structures (Part 2)

Many flowers have long styles and filaments Natural selection favored length because it increases

likelihood of pollination — either making them more accessible to insects, or to catch the wind

Photo 29.27 Monocot flower

(daylily Hemorcallis sp.)

showing flower parts of

perianth in threes


of the Angiosperms?

Perfect flowers:

favors self-pollination, but

usually disadvantageous

many mechanisms have

evolved to circumvent this

problem

bush monkeyflower is

constructed so that two

different hummingbirds must

participate in pollination

http://www.dkimages.com/discover/previews/931/50375608.JPG

Mimulus aurantiacus,

bush monkeyflower


of the Angiosperms?

Figure 29.13 An Unusual Solution to Selfing

Figure 29.14 Stigma Behavior in Mimulus Flowers (Part 1)

Figure 29.14 Stigma Behavior in Mimulus Flowers (Part 2)

Most angiosperms are animal-pollinated by insects, birds, and bats Many flowers entice

pollinators with nectar and pollen

Plants and their pollinators have coevolved

Some relationships are very specific—e.g., one species of moth pollinates one species of yucca plant.

http://bobklips.com/BOBS_WEBSITE/ILF-

YUCCFILAlaying.jpg


of the Angiosperms?

Other pollinators are much

less specific, but even these

have some specialization

Bird-pollinated flowers are

often red and odorless.

Many insect-pollinated

flowers have characteristic

odors, and bee-pollinated

flowers may have

conspicuous markings, or

nectar guides, that may be

visible only to bees with UV

lightFlowers under sunlight and

UV, showing nectar guides


of the Angiosperms?

Angiosperm life cycle:

Zygote develops into an embryo

consists of embryonic axis (will become stem and root), and 1 or 2 cotyledons —seed leaves

Cotyledons absorb and digest endosperm, some become photosynthetic

www.botany.hawaii.edu/faculty/webb/Bot201/Angiosperm/MagnoliophytaLab99

Shepherd's Purse

(Capsella) Embryo, a dicot

cotyledons


of the Angiosperms?

Figure 29.14 The Life Cycle of an Angiosperm

Animation 29.2 Life Cycle of an Angiosperm

Ovary and seeds develop into fruits

Fruit protects seed and aids in dispersal,

(e.g., can become attached to or eaten

by animals)

http://www.hickerphoto.com/data/media/152/kiwi-fruit_3629.jpg


of the Angiosperms?

Types of fruits:

Simple fruits develop from one carpel

Aggregate fruits develop from several

carpels

Simple fruits – cherries

Aggregate fruits –

raspberries


of the Angiosperms?

Multiple fruits form from a cluster of flowers

Accessory fruits develop from parts other than carpels

Multiple fruits –

pineapple

Accessory fruits –

strawberries

http://www.botany.hawaii.edu/faculty/webb/BOT201/Angiosperm/Frui

ts/PineappleYoung240.jpg

Pineapple

flowers


of the Angiosperms?

Figure 29.15 Fruits Come in Many Forms and Flavors

Most angiosperms are in two major clades: Monocots

One cotyledon

Grasses, cattails, orchids, palms

Eudicots (dicots)

Two cotyledons

Majority of familiar flowering plants, most herbs, trees, shrubs

Other clades include star anise and relatives, water lilies, and magnoliids


of the Angiosperms?

Figure 29.17 Evolutionary Relationships among the Angiosperms

• Other clades include star anise and relatives, water lilies, and magnoliids

Figure 29.18 Monocots and Eudicots Are Not the Only Surviving

Angiosperms

Water lilies

Star anise

Avocado

Magnoliid clade

Black pepper Dutchmean’s

pipe

Amborella

trichopoda

Figure 29.19 Monocots

Date palm

Lilies

Wheat

Monocots

Figure 29.20 Eudicots

Prickly pear

cactus

Dogwood

Catclaw Brier

Eudicots

Basal clade of angiosperms is disputed

Two leading candidates used to be the

magnolia family

New molecular data indicates it is Amborella —

a clade consisting of only one species

http://www.biosurvey.ou.edu/okwild/images/Magnolia2.jpg


of the Angiosperms?

Magnolia

grandiflora

29.4 How Do Plants Support Our World?

Plants contribute to ecosystem services:

processes by which environment

maintains resources that benefit humans

Plants are primary producers:

photosynthesis traps energy and

carbon, making them available for their

own needs and for herbivores and

omnivores that consume them, and for

the whole food chain


Plants produce O2 and remove CO2 from

the atmosphere

Contribute to soil formation and soil

fertility

Roots hold soil in place, preventing

erosion

Moderate local climate by increasing

humidity, providing shade, and blocking

wind.

Seed plants are our

primary food source

Twelve are most

important: rice,

coconut, wheat, corn,

potato, sweet potato,

cassava, sugarcane,

sugar beet, soybean,

common bean,

banana

http://scienceafrica.com/cms/wp-content/uploads/2010/06/cassava-ethanol.jpg


http://3.bp.blogspot.com/_vhhw--

dmXBE/SEKkOrSMjVI/AAAAAAAAAtw/E-

3uz7yigtU/s400/biopact_cassava_biofuels.jpg

Cassava root is

an important

food in Africa


Half the world’s

population gets most of

its food energy from

rice (Oryza sativa)

Rice been cultivated

for more than 8,000

years

http://www.equita.qc.ca/images/produits/gn_008.jpg

The coconut palm (Cocos nucifera) is

called the ―Tree of Life.‖

Every above-ground part is used.

http://www.uni-graz.at/~katzer/pictures/coco_12.jpghttp://www.pacsoa.org.au/palms/Cocos/nucifera.jpg


Figure 29.20 The Tree of Life

Many medicines come from

seed plants

Medicines are found by

screening large numbers

of plants, or screening

large numbers of

chemical compounds

Ethnobotanists also

discover medicinal plants

by studying people and

their uses of plants all

over the worldhttp://www.mountainvalleycenter.com/store/images/cherheal.JPG



Extracts of Pacific yew bark (Taxus brevifolia)

showed antitumor activity in rodents

Taxol was isolated, tested, and approved for use

in treating several types of cancer.

http://www.freewebs.com/dicentra/Pacific%20Yew2.jpghttp://www.cas.vanderbilt.edu/bioimages/t/wta

br2-cofemale42577.jpg



Spanish priests in

Peru saw native

people used bark of

Cinchona trees to

treat fevers

The active ingredient,

quinine, was identified

in 1820, and was used

to treat malaria

Quinine is found in

tonic water

http://www.botanical.com/botanical/mgmh/c/calisa08-l.jpg

http://www.wellsj.com/library/images/uv/quinine.jpg

Documents

The Evolution of Seed Plantswtyler-irsc.weebly.com/uploads/1/9/8/6/19866611/ch29_lecture-spr11.pdf · 29 The Evolution of Seed Plants ... Gymnosperms? •29.3 What ... Success of