Seedless Plants and Tracheophytes Notes

Seedless Plants

Cooksonia sp.

  • Earliest vascular plant, approximately 420 million years ago (MYA).
  • Lacks roots and stems, representing a transitional form between bryophytes and tracheophytes.
  • Possesses a spore-bearing capsule.
  • Only the sporophyte generation is known.
  • Presence of vascular tissue (dark stripe).

Tracheophytes

  • Dominant sporophyte generation; vascular plants evolved around 420 MYA.
  • Key evolutionary advancements:
    • Vascular tissue for nutrient transport.
    • Reduced gametophyte generation.
    • Stems and roots enabling larger size.
    • Leaves enhancing photosynthesis.
    • Seeds in some lineages.

Vascular Transport

  • Vascular tissue facilitates nutrient distribution through specialized cells.
    • Xylem: Transports water and dissolved nutrients upwards from the roots.
    • Phloem: Transports sucrose and hormones throughout the plant.

Stems

  • Evolved first, enabling water and food transport via vascular tissue.

Roots

  • Enable larger plant size by:
    • Providing support and anchoring the plant to the substrate.
    • Increasing water uptake to compensate for increased water loss due to larger size and more stomata.
  • Increase surface area for water and nutrient uptake; transport water and food via vascular structures.

Leaves

  • Vascularized structures that enhance photosynthesis by increasing surface area; they evolved multiple times.
    • Lycophyll: Single vascular strand, found in club mosses.
    • Euphyll: True leaves with multiple vascular strands, found in ferns and seed plants.

Leaf Anatomy

  • Vascular structures with photosynthetic tissue in between.
  • Bryophytes lack vascular tissue and true leaves.

Seeds

  • Highly resistant structures protecting plant embryos.
  • Composed of a diploid embryo and food storage within a seed coat.
  • Found only in seeded plants, not in bryophytes, lycophytes, or pterophytes.

Tracheophyte Groups

  • Three main groups:
    1. Club mosses (Lycophytes).
    2. Ferns, Horsetails, and Whisk Ferns (Pterophytes).
    3. Seed plants (Gymnosperms and Angiosperms).

Lycophytes

  • Club mosses are superficially similar to mosses but are vascularized and sporophyte-dominated.
  • Lycophylls: Small, unbranched-veined leaves; specialized leaves form spores via meiosis.

Lycophyte Reproduction

  • Gametophytes are free-living and produce eggs and flagellated sperm.
  • Both sporophyte and gametophyte are photosynthetic.

Pterophytes

  • Includes horsetails, whisk ferns, and ferns.
  • Gametophytes are small and free-living, producing flagellated sperm and eggs on the same gametophyte.

Whisk Ferns

  • Lack roots and leaves but have evenly-forking stems.
  • Some gametophytes develop vascular tissue.

Horsetails

  • Ribbed, jointed photosynthetic stems arising via underground rhizomes.
  • Equisetum is the only living genus.
  • Rhizome: An underground, horizontal stem.

Horsetail Reproduction

  • Spore-producing cone; spores germinate into a free-living photosynthetic gametophyte.

Ferns

  • Most abundant seedless vascular plant with many forms.
  • Leaves: Fronds, which develop at rhizomes as tightly coiled fiddleheads that unroll.
  • Fronds are euphylls, having multiple vascular strands, greatly increasing photosynthetic surface area.

Fern Reproduction

  • Sporangia clustered into sori on the underside of fronds.
  • Gametophyte is small, one cell thick, and heart-shaped; anchored via rhizoids.
  • Antheridia produce flagellated sperm; archegonia provide some protection for the developing embryo.