dr. mitch pavao-zuckerman diversity of plants · 2006-01-26 · 4 vascular plants •the diploid...

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Dr. Mitch Pavao-ZuckermanDepartment of Ecology and Evolutionary Biology

[email protected] hours: Biosciences West 431W and F 1-2 p.m. or by appointment

Diversity of Plants

Diversity of Plants (Fig 29.4)

Ancestral Alga Chlorophyta

Nontracheophytes

Nonseed Tracheophytes

Gymnosperms

Angiosperms

The Transition to Life on Land

The Vascular PlantsThe Seed PlantsThe Flowering Plants

Monophyly• Monophyletic group – includes the

most recent common ancestor and all decendents

• These are NOT monophyletic:

Green Plants(viridiphytes) are a monophyletic group

• Green Plants include the Chlorophytes (green algae)

• Other green algae• and the land plants

Embryophytes (Land Plants)

Land Plants are also a monophyletic group

• Photosynthetic eukaryotes that use chlorophyll a and b and store carbohydrates starch

• Resting embryo with placental connection to the parent.

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The Conquest of the LandHistory of plants on land• 500 mya - a few algae and lichens.• By 460 mya - primitive Land Plants, • By 425 mya - Early Vascular Plants

were common

• How did it happen?• Obstacles?

Fossil

Reconstruction

The Conquest of the Land

2. thick spore wall

Early innovations in land plant evolution:

1. cuticle (waxy coating)

3. Antheridia and archegonia (gamete cases),

4. protected embryo

5. protective pigments – flavonoidsabsorb damaging UV light

Land Plants (Embryophytes) (Fig 29.4)


Nontracheophytes


Gymnosperms

AngiospermsPlant Kingdom?

Protected Embryos

Nontracheophytes:Liverworts, Hornworts, and Mosses

• Small plants (compared to present day shrubs and trees)

• Lack specialized water (xylem) and food conducting tubes (phloem) of vascular plants.

• Rely on diffusion of water and minerals.

Diploid

Haploid

Plant life cycles feature alternation of generations (Fig 29.2)

Haploid (n)

Diploid (2n)

Fertilization

Zygote

Multicellular sporophyte

Meiosis

Spore

Multicellular gametophyte

Gametes

• Diploid generation is smaller than the haploid generation and

• Diploid depends on it for water and nutrition.

• “The big green thing” is the haploid stage.

• The diploid stage is attached to it.

Nontracheophytes:Liverworts, Hornworts, and Mosses

Fig. 29.5

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Liverworts (9,000 species)

• Lack stomates (pores with guard cells that regulate C02 uptake and H20 loss).

• Small spore producing diploid phase compared to hornworts or mosses

Hornworts (100 species)

• Have stomates • Horn-shaped spore producing

diploid stage• One large flat chloroplast per cell

Mosses (15,000 species)

• Have stomates • Spore producing upright diploid

stage with capsule• Capsule has a lid and row of teeth

that release the spores in wet weather.

a. They are all relatively small

b. They all lack specialized conductive tissue such as xylem and phloem

c. All possess stomata for gas exchange

d. The big generation is haploid (one set of chromosomes) with the smaller diploid (two sets of chromosomes) generation attached and dependent.

What is not a common feature of non-vascular plants?



Nontracheophytes


Gymnosperms

Angiosperms

Vascular Plants

(Tracheophytes)

Protected Embryos

Vascular tissue

Vascular Plants• Thick-walled dead water-conducting

cells.more efficient water movementsupport for tall plants.

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Vascular Plants • The diploid generation became LARGER and

independent of the haploid generation.

Figure 28.19

Figure 29.20

Tracheophytes

• The earliest tracheophytes lacked roots.

• Roots – possibly evolved from branches

Tracheophytes • Simple leaves may have

evolved from the spore producing structures.

• Complex leaves may have evolved from a branching stem system.

Difference?



Nontracheophytes


Gymnosperms

Angiosperms

Vascular Plants

(Tracheophytes)

Protected Embryos

Vascular tissue

Nonseed TracheophytesClub mosses 1,200 species

• Simple leaves• Cone-like structures with spores.• Dominated tropical coastal swamps in

Carboniferous period 300 mya coaldeposits.

• Selaginella is common here in the desert.

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Nonseed Tracheophytes Whisk Ferns 15 species• Simple branching like ancient vascular plants. • Tiny simple leaves• No true roots

Reconstruction of ancienttracheophyte

Tracheophytes Horsetails 15 species

• Jointed hollow stems • Silica deposits (“scouring rush”)• Leaves in whorls• Spore sacs under “shields” on

“cones”

Nonseed Tracheophytes Ferns 12,000 species• Big complex leaves with branching veins • Spores in sacs clustered on the bottom of

the leaf• Leaves unfold from “fiddlehead”

•Tree ferns can reach 60 ft

a. They are larger than non-vascular plants

b. They possess specialized cells for moving water and food

c. All possess stomata for gas exchange

d. The big generation is haploid (the gametophyte with one set of chromosomes)

What is not a common feature of Non-Seed Tracheophytes?



Nontracheophytes


Gymnosperms

AngiospermsSeed plants

Protected Embryos

Vascular tissue

Seeds

Seed Plants 300,000 species

• The seed plants have greatly reduced haploid stage.

• How did this happen?

Fig 30.2

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• Further reduced haploid generation.

Part of the evolution of seedsand pollen.

• Seeds - protected resting stage opening many possibilities, like suspended animation.

•Pollen - sperm delivery system; escape the need of water for sperm to swim.

How did seeds evolve?• Ancestors of seed plants had one kind of spore.

Spore sac

• First dimorphic spores evolved:Microspores (grow into sperm producing haploid stage)Megaspores (grow into egg producing haploid stage)

• Megaspores reduced to just one.

How did seeds evolve?• Megaspore enveloped in a sac.

• Female haploid stage grows in this “seed”.

• It is attached to the diploid parent.

Pollen is a reduced male haploid stageDiploid

Spore sacHaploid Spores

Reduced haploid stage

Plant and flower are diploid

Pollination1. Pollen reduced haploid female. 2. Pollen produce sperm to fertilize an egg.3. The zygote develops into a seed embryo.


• So, seed plants make seeds and pollen

• Also make wood.

• Evolved ~ 370 mya

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Nontracheophytes


Gymnosperms

Angiosperms

Protected Embryos

Vascular tissue

Seeds

Seed Plants - Gymnosperms

• Gymnosperm = ‘naked seeded’• Do not have flowers or fruit tissue

Gymnosperms - 4 PhylaCycads Ginkos

Gnetophytes

Gymnosperms - Conifers

• Leaves often “evergreen” needles or scales

• Cones: scales with seeds

Seed Plants- Conifers • Longest-lived trees - Bristlecone

pine: 5,000y• Tallest tree – redwood 112 m• Most massive tree – sequoia – 11m

wide



Nontracheophytes


Gymnosperms

Angiosperms

Flowering Plants

Protected Embryos

Vascular tissue

Seeds

Flowers

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Seed Plants - Angiosperms

• Highly diverse plant phylum• Dominant form of plant life on Earth

• Because of differences from other plants

Seed Plants - Angiosperms Pollination• Pollen lands on stigma, rather than at the

tip of the ovule• Reduces chance of self-pollination –

increases genetic diversity

Fig 30.7, 30.11

Double fertilization (producing zygote and endosperm)

• Flowers and fruit are unique features

Endosperm Nucleus

Seed Plants Angiosperms

• Fruit and stamens evolved from leaf-like structures.

Seed Plants - Angiosperms

• Much diversity is related to pollination anddispersal mechanisms.

Seed Plants Angiosperms

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Review Land Plants (Fig 29.4)


Nontracheophytes


Gymnosperms

Angiosperms

Protected Embryos

Vascular tissue

Seeds

Flowers Plant Kingdom?

Tracheophytes?

Seed plants?

dr. mitch pavao-zuckerman diversity of plants · 2006-01-26 · 4 vascular plants •the diploid...

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