Diversity of Plants

Diversity of Plants

  • Evolution from Green Algae:
    • Land plants evolved from green algae, specifically Chlorophytes and Charophytes.
    • Key similarities include:
    • Both have cellulose-synthesizing proteins
    • Structure of flagellated sperm
    • Formation of the cell plate during mitosis
    • Note: Green algae are not a monophyletic group; they form the clade Viridiplantae.

Typical Plant Characteristics

  • Autotrophic: Produce their own food via photosynthesis.
  • Cell walls: Composed of cellulose.
  • Storage carbohydrate: Primarily starch.
  • Haplodiplontic life cycle: Involves two multicellular stages (gametophyte and sporophyte).
  • Body Organization: Consists of three organ types (roots, stems, leaves), each made of three tissue types.
  • Dependent multicellular embryos: All land plants have embryos that develop within gametophytes.
  • Tissue development: Arises from apical meristems (growth regions).

Plant Life Cycle

  • Alternation of Generations:
    • Alternates between haploid gametophyte phase and diploid sporophyte phase.
  • Process involves:
    • Fertilization: Fusion of sperm and egg.
    • Mitosis: Develops the zygote into a sporophyte.
    • Meiosis: Leads to spore production.
    • Germination: When spores develop into gametophytes.

Body Plans of Plants

  • Gametophyte Generation:
    • Germinates from spores and generally lacks vascular tissue/waxy cuticle.
    • Has structures for gametes production: archegonia (female) and antheridia (male).
  • Sporophyte Generation:
    • Grows from a zygote and may have vascular tissue.
    • Produces spores in a specialized structure, the sporangium.

Plant Body Structure

  • Organ Types:
    • Roots: Below ground system.
    • Stems (Shoots): Above ground, support for leaves and flowers.
    • Leaves: The main site for photosynthesis.
    • Flowers or Cones: Reproductive structures.
  • Vascular Tissue: Transports water (xylem) and nutrients (phloem).
  • Waxy Cuticle: Protects against water loss.

Plant Diversity

  • Approximately 300,000 plant species documented.
    • Major plant phyla include:
    • Hepatophyta (liverworts)
    • Bryophyta (mosses)
    • Lycophyta (clubmosses)
    • Coniferophyta (conifers)
    • Monilophyta (ferns)
    • Anthophyta (flowering plants)

Evolution of Land Plants

  • Originated from green algae.
  • Nonvascular Plants: Considered basal plants, including hepatophytes and bryophytes.
  • Seedless Vascular Plants: Comprised of lycophytes and monilophytes.
  • Seed Plants: Further divided into gymnosperms (non-flowering) and angiosperms (flowering).

Nonvascular Plants

  • Phylum Hepatophyta:

    • Liverworts with a dominant gametophyte body plan.
    • Dioecious; with separate male and female gametangia.
    • Minimal vascular tissues; rely on diffusion for water and nutrient transport.

  • Phylum Bryophyta:

    • Mosses featuring protonema (initial growth form).
    • Dioecious; relies on moisture for sperm transfer.

Seedless Vascular Plants

  • Phylum Monilophyta:
    • Includes ferns and horsetails.
    • Possess true vascular tissues for efficient water and nutrient transport, supporting larger body structures.
    • Fertilization occurs in the archegonium, where sporophytes develop.

Heterospory and Seed Plants

  • Seed plants produce two distinct sizes of spores:
    • Microspores (male) and macrospores (female).
    • Male represented by pollen grains, transferring sperm without needing water for fertilization.
    • Ovule develops into seed after fertilization, remaining enclosed within ovule tissue until the seed is fully formed.

Gymnosperms

  • Phylum Coniferophyta:
    • Cone-bearing plants, known for their needle-like leaves and thick cuticles.
    • Depend on wind and animal pollination for reproductive success.

Angiosperms

  • Phylum Anthophyta:
    • Includes flowering plants with seeds enclosed within fruit; extremely diverse.
    • Characterized by variable lifespans, from annuals to perennials, found in various ecosystems.