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Green Algae & Land Plants

  • Viridiplantae (Green Plants): Includes green algae (traditionally protists, clues to terrestrial transition) and land plants (first terrestrial organisms).

  • Importance of Green Plants:

    • Backbone of terrestrial ecosystems: oxygen production, soil production, moisture retention, erosion prevention, climate moderation.

    • Primary producers: convert solar energy into chemical energy; pivotal in carbon cycle.

  • Human Uses:

    • Food, fuel, fiber, and medicines derived from plants; significant sources for prescription drugs.

  • Phylogeny:

    • Green algae linked to land plants through similar chloroplast structures and biochemical compositions.

    • Major groups include:

    • Green Algae: Ulvophyceae, Charophyceae, Coleochaetophyceae, Zygnematophyceae.

    • Land Plants: Non-vascular (Hepaticophyta, Bryophyta, Anthocerophyta) and vascular plants (Lycophyta, Pteridophyta, Equisetophyta, gymnosperms, angiosperms).

  • Aquatic to Terrestrial Transition:

    • Enhanced light and CO2 availability; challenges included water loss and UV radiation.

    • Adaptations: evolution of cuticle, stomata, and UV-absorbing compounds.

  • Reproductive Strategies:

    • Land plants have features like resistant spores (sporopollenin) and gametangia for gamete protection.

    • Food/nourishment of embryos on the parent plant; alternation of generations (gametophyte and sporophyte phases).

  • Non-Vascular Plants:

    • Dominant gametophyte phase; lack of vascular tissues; dependence on flagellated sperm for fertilization.

    • Main groups include liverworts (Hepaticophyta), mosses (Bryophyta), and hornworts (Anthocerophyta).

  • Vascular Plants:

    • Dominance of sporophyte phase; true roots, leaves, and evolution of lignin for structural support and water transport.

    • Groups include lycophytes, whisk ferns, and ferns.

  • Seed Plants:

    • Gymnosperms (no ovary) and angiosperms (ovary present); efficient reproductive strategies through pollen and seeds.

    • Major types include Ginkophyta (Ginkgo), Cycadophyta (cycads), Cupressophyta (redwoods), Pinophyta (pines), and Gnetophyta (Gnetum).