Evolution of plants

Below is a barebones overview of the evolution of plants, based on notes from a module in the University of Copenhagen's Origins: Formation of the Universe, Solar System, Earth and Life. For additional information, check here and here.

Evolution of plants. Image credit: M. J. Farabee

Image credit: M. J. Farabee

Features of plants

  • Ordovician (450 Mya): plants evolved from green algae living continental freshwater ponds
  • Harsh environmental conditions on land drove the evolution of land plants
    • Limited water
      • Reproduction
        • Spores: coated male gametes protect against dessication and strong UV light
          • Oldest spore discovered: 450 million years old, deposited in marine sediments after rivers transported it from the land to the sea
        • Seeds: appeared in the late Devonian; parent provides egg cell with protection and nutrients
      • Roots and vascular systems: allow plants tap deeper water supplies and transport water and nutrients
        • First vascular plant fossils found from the early Devonian (420 Mya)
          • Simple, forked branches with spores at tip; lacked leaves (entire plant was photosynthetic); inhabited moist areas
      • Cuticle: waxy outer layer minimizes evaporative water loss
        • Require stomata, breathing holes, to allow uptake of carbon dioxide
    • Gravity
      • Lignin: rigid material in plant cell walls that allows plant stems to stand upright, which facilitates capture of sunlight
      • Roots also help support plants

Major vascular plant groups

  • Spore plants
    • Lycophytes (club mosses)
      • Appeared in the early Devonian
      • Small herbaceous plants and oldest extant vascular plants
      • Devonian Sigillaria reached 45 m tall and formed vast swamp forests
    • Ferns
      • Appeared in late Devonian
      • Developed large lobed leaves to capture sunlight
      • Ranged in size from small ephiphytic (lives on other plants) plants to large trees
      • Exploited understorey habitats
  • Seed plants
    • Gymnosperms
      • Conifers
        • Seeds in cones
        • Wind-pollinated
        • Wollemia: modern plant with pollen from the Cretaceous
      • Cycads
        • Woody, barrel-shaped trunk with crown of large, stiff, evergreen leaves
        • Common in the Jurassic; three families alive today
      • Gingkos
        • Fan-like leaves with numerous non-crossing parallel veins
        • Widespread during the Jurassic; one species (found in China) alive today
    • Angiosperms: flowering plants
      • Largest plant group in modern times
      • Oldest fossil pollen from the Cretaceous (136 Mya)
      • Petals and sepals developed from leaves
      • Rely on insects, birds, bats for pollination
      • Seeds enclosed in carpels
Cortney

About Cortney

Geology lover. Proud owner of a 2014 Honda CRF250L. Grew up on NES, N64, & Gameboy. Collects maneki neko (lucky cats). Married to a gearhead. Email cortney@luckysci.com. Wishlist.

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