Plant Evolution Notes

Highlights of Plant Evolution

  • Non-vascular plants are commonly called bryophytes.
  • Bryophytes are not a monophyletic group.
  • Relationships among bryophytes and vascular plants remain unresolved.

Everyday Uses of Plants

  1. Food (20 amino acids)
  2. Oxygen
  3. Wood (building materials)
  4. Medicines
  5. Clothes

Ecological and Economic Importance of Mosses

  • Capable of inhabiting diverse and extreme environments.
  • Common in moist forests and wetlands.
  • Some mosses retain nitrogen in soil and contribute to nutrient cycling.
  • Sphagnum (peat moss) forms peat, a source of fuel and an organic carbon reservoir.
  • Sphagnum also acidifies the soil.

Key Definitions

  • Sporophyte: Multicellular diploid form of the plant body.
  • Gametophyte: Structure that produces haploid gametes in plants.
  • Sporangium: Where meiosis occurs and haploid spores develop.
  • Antheridia: Male gamete development structure.
  • Archegonia: Female gamete development structure.

Main Traits of Bryophytes

  • Dominant gametophytic phase (1n).
  • Lack xylem and phloem, roots, and leaves.
  • No cuticle present.
  • Sporophyte is dependent on female gametophyte for nutrition.

Moss Life Cycle

  • Tiny haploid spores inside capsules.
  • Wind dispersal mechanism.
  • Spores develop into male and female gametophytes.
  • Rhizoids anchor the body and assist in nutrient transfer.
  • Flagellated sperm produced in antheridia swims to fertilize egg in archegonium.
  • Life cycle exhibits alternation of generations.

Bryophyte Sporophyte Structure

  • Composed of:
    • Foot: Receives nutrients from female gametophyte.
    • Seta: Elongated stalk.
    • Sporangium: Site of meiosis (2n to 1n spores).
  • Hornworts and moss sporophytes have stomata for gas exchange; liverworts do not.

Liverworts (Hepatophyta)

  • Liver-shaped or leafy gametophytes.
  • Smallest sporophytes; male and female gametangia on separate plants.
  • Archegonia and antheridia on elevated gametophores.
  • Miniature sporophytes can be found on female gametangia undersurface.
  • No stomata; fast-growing.

Hornworts (Anthocerophyta)

  • Non-vascular plants in damp environments.
  • Horizontal gametophytes with long tapered sporophytes.
  • No seta, only sporangium present.