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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
Extant Land PlantsPinophyta - gymnosperms
• 870 species• seed plants but seeds naked orexposed• often divided into 4 phyla
conifers
Extant Land PlantsPinophyta - gymnosperms
• 870 species• seed plants but seeds naked orexposed• often divided into 4 phyla
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Pinophyta - gymnosperms
• 870 species• seed plants but seeds naked orexposed• often divided into 4 phyla
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
Age of the earth = 1 calendar year4.6 billion years = 365 days
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
Age of the earth = 1 calendar year4.6 billion years = 365 days
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
Age of the earth = 1 calendar year4.6 billion years = 365 days
First eukaryotes - 1.5 bya= early September (2/3 of earth timegone)
Earth Time
Age of the earth = 1 calendar year4.6 billion years = 365 days
First abundant fossils in Cambrian“explosion” - 560 million years agoMany phyla of animals= early November
Burgess Shale
Earth Time
Age of the earth = 1 calendar year4.6 billion years = 365 days
First land life in Ordovician - 460mya (a liverwort?)= November 15 (7/8ths of earth timegone!)
Spore Tetrad
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Earth Time
Age of the earth = 1 calendar year4.6 billion years = 365 days
First angiosperm Jurassic/Cretaceous- 135 mya= December 21!
Earth Time
Age of the earth = 1 calendar year4.6 billion years = 365 days
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)
Extinct Land Plants - the Fossil Record
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
Early Devonian Period (410 - 390 mya)
Extinct Land Plants - the Fossil RecordEarly Devonian Period (410 - 390 mya)
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:
Extinct Land Plants - the Fossil Record
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• underground axis (root) and aboveground photosynthetic stem
• rhizoids (water uptake)
Extinct Land Plants - the Fossil Record
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:
Early Devonian Period (410 - 390 mya)• underground axis (root) and aboveground photosynthetic stem
• rhizoids (water uptake)
• primitive leaves
Extinct Land Plants - the Fossil Record
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:
Early Devonian Period (410 - 390 mya)
• underground axis (root) and aboveground photosynthetic stem
• rhizoids (water uptake)
• primitive leaves
• internal transport - vascular tissue
Rhynia
Extinct Land Plants - the Fossil Record
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:
Early Devonian Period (410 - 390 mya)• underground axis (root) and aboveground photosynthetic stem
• rhizoids (water uptake)
• primitive leaves
• internal transport - vascular tissue
• epidermis, cuticle, stomates
Rhynia
Extinct Land Plants - the Fossil Record
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:
Early Devonian Period (410 - 390 mya)
10
• support tissue - lignin
• shift to sporophyte dominantrather than gametophyte dominant
• sporopollenin to cover spores forprotection
• underground axis (root) and aboveground photosynthetic stem
• rhizoids (water uptake)
• primitive leaves
• internal transport - vascular tissue
• epidermis, cuticle, stomates
gametophyte
sporophyte
Extinct Land Plants - the Fossil Record
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:
Early Devonian Period (410 - 390 mya)
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:
• support tissue - lignin
• shift to sporophyte dominantrather than gametophyte dominant
• sporopollenin to cover spores forprotection
• underground axis (root) and aboveground photosynthetic stem
• rhizoids (water uptake)
• primitive leaves
• internal transport - vascular tissue
• epidermis, cuticle, stomates
• embryo
Extinct Land Plants - the Fossil RecordEarly Devonian Period (410 - 390 mya)
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)
Extinct Land Plants - the Fossil Record
11
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)
Extinct Land Plants - the Fossil Record
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
Extinct Land Plants - the Fossil Record
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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
Extinct Land Plants - the Fossil Record
“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)
Extinct Land Plants - the Fossil Record
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