land plant evolution: ancestors of land plants algae to...

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Land Plant Evolution:Algae to Angiosperms

The greatest adaptive radiation . . .

• is the largest radiationof plants

• involves series ofdramatic adaptations tothe problem of living onland and being non-motile

• exhibits successiverounds of speciation andsubsequent extinction

• sets the stage for thedevelopment of a land-based ecosystem withfungi and animals

. . . a nearly 500 million year story

. . . for the evolution of Hordeum and Humulus

. . . a nearly 500 million year wait

Land Plant Evolution:Algae to Angiosperms

The greatest adaptive radiation . . .

• know the basic extant land plant lineages today

• understand the general (not the details) series of events andtiming of the rise and fall of extinct land plant lineages

• know some of the adaptations for land plant life that arose fromOrdovician to Devonian

• understand the basic arguments on the 4 phylogenetic issuesrelating to land plant evolution

• Ancestors of land plants

• Base of land plants

• Base of vascular plants

• Relationships among seed plants

Ancestors of Land Plants

Green Plants are here

• land plants are in a largerlineage of green plants withinPlantae

• a single endosymbiotic eventgave rise to plastids

• land plants are derived fromthe green algae lineage

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Bryophyta - bryophytes

• 16,000 species• nonvascular plants, primitive land plants• gametophyte dominant• comprising 3 main groups (often 3 phyla)

liverworts

mosses

hornworts

Extant Land Plants

Lycopodiophyta - lycopods

• 1,150 species• vascular plants, primitive vascular plants• sporophyte dominant; free sporing• comprising 3 families

spikemoss

quillwort

club moss

Extant Land Plants

Equisetophyta - horsetails, scouring rushes

• 15 species in Equisetum• vascular plants, reduced leaves, terminalsporangia• sporophyte dominant; free sporing

Extant Land Plants

Psilophyta - whisk ferns

• 6 species in two genera• vascular plants, leafless green stemmed, lateralsporangia• once considered most primitive extant land plant

Extant Land Plants

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Polypodiophyta - ferns

• 11,000 species• diverse in habit and habitat• spores produced in specialized sporangia

Extant Land Plants

ginkgo

Extant Land PlantsPinophyta - gymnosperms

• 870 species• seed plants but seeds naked orexposed• often divided into 4 phyla

cycads



conifers



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Pinophyta - gymnosperms


gnetophytes

Extant Land Plants

Magnoliophyta - angiosperms, flowering plants

• 275,000 species• tremendous adaptive radiation on land• seed plants with seeds encased in ovary• flowers a “key innovation”

Extant Land Plants

Earth Time

Age of the earth = 1 calendar year4.6 billion years = 365 days

Earth forms at 4.6 bya= January 1, 12:00 a.m.

A different perspective beforetaking a look at the rise and fallof land plant lineages throughtime . . .

Earth Time


First evidence of life - 3.8 byaOldest fossils - 3.5 bya= late March (1/4 of earth time gone)

Stromatolites - CaCO3 ppt by cyanobacteria= photosynthesis!

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Earth Time


O2 accumulates in atmosphere -2.0 bya= late July (>1/2 of earth time gone)

CO2

+

H2O

Starch

+

O2

reducingatmosphere

oxidizingatmosphere

anaerobeextinction

aerobeevolution

Earth Time


First eukaryotes - 1.5 bya= early September (2/3 of earth timegone)

Earth Time


First abundant fossils in Cambrian“explosion” - 560 million years agoMany phyla of animals= early November

Burgess Shale

Earth Time


First land life in Ordovician - 460mya (a liverwort?)= November 15 (7/8ths of earth timegone!)

Spore Tetrad

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Earth Time


First angiosperm Jurassic/Cretaceous- 135 mya= December 21!

Earth Time


First human civilization (centered onbeer production?) & formation ofGreat Lakes flora/vegetation= December 31, 11:59pm.!

Barley harvest, Mesopotamia 7000ya

Extinct Land Plants - the Fossil RecordOrdovician Period (505 - 440 mya)

• First evidence of land life at 460 mya

Microfossils of sporeswith sporopollenin(degradation resistantmaterial like lignin) andsimilar to modern daybryophytes such asliverworts

Found worldwide in shales that weredeposited at the marine-terrestrialinterface

Glomales fungi seen in 460 myWisconsin rock. Glomales today formimportant arbuscular mycorrhizalassociations with some liverworts andhornworts and many vascular plants.Symbiosis!

Extinct Land Plants - the Fossil RecordOrdovician Period (505 - 440 mya)

• Other evidence of land life

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Ordovician Period (505 - 440 mya)

• Other evidence of land life

Manitobia patula thallus from Canada- an aquatic charophyte algae

Extinct Land Plants - the Fossil Record Extinct Land Plants - the Fossil Record

Cooksonia fossils are seen in the midSilurian growing close to water

Silurian Period (440 - 410 mya)

Cooksonia fossils are seen in the midSilurian growing close to water

• very simple, stick-like,leafless plants but sporophytedominant

• no roots are seen

• terminal sporangia (sporeproducing structures)

• possibly non-vascular

Extinct Land Plants - the Fossil RecordSilurian Period (440 - 410 mya) Silurian Period (440 - 410 mya)

Late Silurian is also the first occurrence ofland animals - arachnids, centipedes

These are predators and thus indicate thatthere were unknown herbivores - communityof plants, herbivores and carnivores!

Silurian view Spider in chert

Extinct Land Plants - the Fossil Record

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Rhynia seen in the early Devonian (RhynieChert fossil) is more complex than Cooksonia(part of Rhyniophytes)

20 cm tall, no roots, no leaves, primitivevascular tissue

Extinct Land Plants - the Fossil RecordEarly Devonian Period (410 - 390 mya)

Rhynia seen in the early Devonian (RhynieChert fossil) is more complex than Cooksonia(part of Rhyniophytes)

20 cm tall, no roots, no leaves, primitivevascular tissue

Rhynia and other Rhynie Chertplants were infected with thefungus, Paleomyces, indicatingextensive mycorrhizalrelationships

Early Devonian Period (410 - 390 mya)


Zosterophyllum seen in the early Devonian isa lycopsid

Clonal plant with reticulating stems, andlateral sporangia as in the shining club moss

Huiperzia lucidula - shining club moss



The Early Devonian lasted some 30 millionyears after the first appearance in mid-Silurianof simple land plants

During this interval the critical characteristicsof land plant survival evolved:


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• underground axis (root) and aboveground photosynthetic stem

• rhizoids (water uptake)




Early Devonian Period (410 - 390 mya)• underground axis (root) and aboveground photosynthetic stem


• primitive leaves








• internal transport - vascular tissue

Rhynia




Early Devonian Period (410 - 390 mya)• underground axis (root) and aboveground photosynthetic stem




• epidermis, cuticle, stomates

Rhynia





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• support tissue - lignin

• shift to sporophyte dominantrather than gametophyte dominant

• sporopollenin to cover spores forprotection






gametophyte

sporophyte







• support tissue - lignin

• shift to sporophyte dominantrather than gametophyte dominant

• sporopollenin to cover spores forprotection






• embryo


First “progymnosperms” [Archaeopteris] -free sporing like ferns and relatives but treeslike gymnosperms with complex leaves -megaphylls

First true ferns [Protopteridium] - free sporingwith complex sporangia & megaphylls

Extinct Land Plants - the Fossil RecordLate Devonian Period (390 - 360 mya) Late Devonian Period (390 - 360 mya)

First “seeds” - “seed ferns” [Archaeosperma]

Plants fern-like with dissected compound leaves,but produce naked seeds (embryo withinprotective coverings)


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The tropical equatorial coal swamps weredominated by a diversity of lycopsids(Lycopodiophyta) and sphenopsids(Equisetophyta)

Lepidodendron (lycopod) was 30 mtall with 1 meter long “microphyll”leaves

Extinct Land Plants - the Fossil RecordCarboniferous Period (360 - 286 mya) Carboniferous Period (360 - 286 mya)

The tropical equatorial coal swamps weredominated by a diversity of lycopsids(Lycopodiophyta) and sphenopsids(Equisetophyta)

Calamites was one of the dominantlarge tree-like horsetails (sphenopsid)


Pangaea begins to coalesce

South of the tropical flora dominatedby lycopsids, sphenopsids, and seedferns existed the Glossopterid flora

• Big trees with net-veined leaves

• Seed bearing (derived from femalegametophyte) and pollen forming(from male gametophyte)

Extinct Land Plants - the Fossil RecordPermian Period (286 - 245 mya) Permian Period (286 - 245 mya)

• Biogeographically ties together flora ofGondwana


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Triassic Period (245 - 208 mya)

Triassic

The Triassic (and Jurassic) isknown as the “Age of Cycads”as this gymnosperm grouprapidly diversified afterinitially appearing earlier inthe Permian.

Modern cycad - Dioon

Extinct Land Plants - the Fossil RecordTriassic Period (245 - 208 mya)

Triassic

• The big trees of the Triassicwere primitive lineages ofconifers and ginkgoes

• The gymnosperms replacedlycopsids and sphenopsids whichwere reduced in size and diversity

• The Petrified Forest NationalPark originated during the lateTriassic


“Age of Dinosaurs” (and Cycads)

Triassic

The Jurassic saw an increase not only ingymnosperm groups such as the cycadsand ginkgoes, but also extinct lineagesBennettitales and relatives likePentoxylon. These plants produced leavesthat superficially resembled cycad leaves.

Williamsonia

Extinct Land Plants - the Fossil RecordJurassic Period (208 - 146 mya)

“Modern” genera are firstseen for Ginkgo . . .

Extinct Land Plants - the Fossil RecordJurassic Period (208 - 146 mya)

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Jurassic Period (208 - 146 mya)

“Modern” genera are firstseen for Ginkgo andEquisetum (horsetail)


Triassic

Near the Jurassic/Cretaceous border, thefirst Angiosperms are seen

Archaefructus

Extinct Land Plants - the Fossil RecordCretaceous Period (146 - 65 mya)

Cretaceous Period (146 - 65 mya)

Although not a strict co-evolution, as insects grouphad already diverged by the Cretaceous, therelationship between insects and flowering plantsfor pollination purposes and herbivore interactionsspurred speciation in both groups

Extinct Land Plants - the Fossil Record Molecular Phylogeny of Land Plants

• land plants are most closelyrelated to the Charales withinthe Charophytes (Karol et al.2001 - Science)

1. Ancestors of land plants?

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Bryophyta - bryophytes

liverworts

mosses

hornworts

Molecular Phylogeny of Land Plants2. Base of land plants? 2. Base of land plants?

• Hornworts are closest tovascular plants (Qiu et al., inpress)

• photosynthetic sporophyteis shared derived character

Molecular Phylogeny of Land Plants

3. Base of vascular plants?

• Lycopods are sister to restof vascular plants

• Whisk ferns and horsetailsare just strange primitiveferns!

Molecular Phylogeny of Land Plants4. Gymnosperms paraphyletic?

• Gnetophytes are not relatedto angiosperms

• Gnetophytes may berelated to Pinaceae!

Welwitschia(Gnetophyte)

Molecular Phylogeny of Land Plants

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Concluding thoughts . . . Concluding thoughts . . .

. . . and thanks for being a great class!

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