Trends in Green Plant Evolution

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Trends in Green Plant Evolution

• Tyson Sacco
• BioG 106 Cornell University

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What are green plants?

• Kingdom Viridiplantae (?) or Chlorophyta
  Plantae
• Monophyletic group
• Green algae land plants

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A Phylogeny of Green Plants
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What features unite all green plants?

• Chloroplasts contain chlorophyll a and b and
  ?-carotene
• Red algae a and phycoerythrins
• Brown algae a, c and xanthins
• Cell walls made of cellulose
• Red cellulose and agar/carageenan
• Brown cellulose and algin
• Synthesize starch to store sugars
• Red floridean starch
• Brown laminarin

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The Big Picture

• Algae is a polyphyletic group
• Green Plants is monophyletic
• Photosynthesis arose in eukaryotes via primary
  endosymbiosis
• Spread among lineages through multiple secondary
  endosymbiotic events

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Major Events in Green Plant Evolution

• 1. Origin of green plants 725 mya
• Oxygen revolution begins

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Major Events in Green Plant Evolution

• 2. Plants colonize land 475 mya
• Evolve from multicellular, freshwater green algae
  like Chara

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Chara
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Major Events in Green Plant Evolution

• 3. Plants adapt to dry environments 400 mya
• Vascular tissue, roots, leaves appear

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Major Events in Green Plant Evolution

• 4. Seed plants evolve 275 mya
• Gymnosperms appear in fossil record

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Major Events in Green Plant Evolution
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Trends in Green Plant Evolution

• Shifting Life Histories
• Adaptations for Terrestrial Life
• Deal with Dry Conditions
• Reproduction on Land

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Shifting Life Histories

• No or Variable Dominance
• Homospory
• Green Algae

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Green AlgaeLife Cycle
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Shifting Life Histories

• Gametophyte Dominance
• Homospory
• Mosses and Liverworts

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Bryophyte Life Cycle
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Shifting Life Histories

• Sporophyte Dominance
• Homospory
• Ferns
• Heterospory
• Conifers, and Flowering Plants

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Pterophyte Life Cycle
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Pine Life Cycle
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Angiosperm Life Cycle
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Terrestrial Life
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Adaptations for Terrestrial Life

• Deal with Dry Conditions
• Problem
• Prevent Water Loss from Cells
• Solution
• Waxy Cuticle - Waterproof Barrier Coating Plant
  Tissues

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Adaptations for Terrestrial Life

• Deal with Dry Conditions
• Problem
• All Cells Need Access to CO2
• Solution
• Stomata - Controlled Openings in Cuticle-Covered
  Surface

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Cuticle and Stomata
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Adaptations for Terrestrial Life

• Deal with Dry Conditions
• Problem
• All Cells Need Access to H2O, This Could Limit
  Them Structurally
• Solution
• Vascular Tissue and Vertical Growth

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Vascular Tissue and Vertical Growth
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Adaptations for Terrestrial Life

• Terrestrial Reproduction
• Problem
• Flagellated Sperm Need Water to Swim to Egg
• Solutions
• Stay in Wet Environments or Disperse Male
  Gametophyte (Pollen Grain)

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Adaptations for Terrestrial Life

• Terrestrial Reproduction
• Problem
• If Fertilization Takes Place On or Within Parent
  Plant, How Can Young Be Dispersed?
• Solution
• Evolve Seeds - Structures That Enclose and
  Protect Developing Embryo

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Pollen and Seeds
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Adaptations for Terrestrial Life

• Terrestrial Reproduction
• Problem
• What If the Wind Doesnt Cooperate?
• Solution
• Evolve Flowers - Establish Relationships with
  Animals to Make Pollination More Likely

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Adaptations for Terrestrial Life

• Terrestrial Reproduction
• Problem
• Wind and Water May Not Reliably Move Seeds to
  Suitable Environments
• Solution
• Evolve Fruit - Establish Relationships With
  Animals That Offer Preferred Dispersal
  Capabilities

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Flowers and Fruit
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In Lab and After

• Short Quiz - focus on lab guide reading,
  especially life cycles and characteristics of
  major groups
• Tour through Green Plants in lab
• Cover more material on algae in Demo after lab
• Lab Practical - Thurs/Fri 4/29, 4/30

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Pollination and Dispersal Strategies
Meganosed Fly Pollination Guild