Seedless Vascular Plants

Tracheophytes/Vascular Plants

• Seedless (4 phyla): Pterophyta, Sphenophyta, Psilotophyta, Lycophyta
• Seed-bearing (5 phyla): Cycadophyta, Ginkgophyta, Gnetophyta, Coniferophyta, Anthophyta

Main Characteristics of Tracheophytes

• Vascular tissue: Allows plants to attain great heights.
• Lignin: Strengthens xylem tissue.
• Gametophyte: Progressive reduction in size and dominance; only a thallus.
• Sporophyte: Progressive increase in size and complexity.

Seedless Vascular Plant Characteristics

• Mostly in moist, cool, shaded places.
• Mostly herbaceous
• Xylem: Tracheids for water transport.
• Sporophyte: Large, free-living, independent.
• Gametophyte: Bisexual, small, thallus, free-living, independent at maturity.
• Leaves: Mostly microphylls (except ferns with megaphylls).
• Seedless, dispersed by spores.
• Mostly homosporous, few heterosporous.
• Antheridia and archegonia present.
• Flagellated sperms: Require water for swimming.

Lycophyta (Club Mosses)

• Examples: Lycopodium, Selaginella (mostly in wet tropical forests).
• Sporophyte: Microphylls, stems (aerial and rhizome), roots.
  • Roots branch dichotomously.
  • Rarely exceed 1m in height.
  • Stems/roots: Protostele.
  • Sporangia borne on sporophylls in strobilus/cone.
  • Cones at apex of stems.
• Homosporous types produce bisexual gametophytes.
• Heterosporous (e.g., Selaginella) produce microgametophytes and megagametophytes.
• Biflagellate sperms
• Subterranean/aerial gametophyte

Heterospory

• Megaspore (n) → Megagametophyte (♀) → Eggs (n)
• Microspore (n) → Microgametophyte (♂) → Sperm (n)
• Meiosis in spore mother cells (2n) in sporangia (2n) produces spores (n).
• Fertilization: Zygote (2n).
• Zygote (2n) → Embryo (2n) → Sporophyte (2n).

Psilotophyta (Whisk Ferns)

• Two genera: Psilotum, Tmesipteris.
• Sporophyte:
  • Lacks roots and leaves (small scales).
  • Aerial stems and subterranean rhizome (dichotomous branching).
  • Rhizoids present on rhizome stems and gametophyte.
  • Protostelic stem.
  • Homosporous.
  • Sporangia in groups of threes at branch tips.
  • Bisexual underground gametophyte.
  • Multiflagellated sperms.

Sphenophyta (Horse Tails)

• One genus: Equisetum (15-25 species).
• Sporophyte:
  • Aerial and rhizome stems.
  • Perennial rhizomes bear adventitious roots.
  • Siphonostelic aerial stems with nodes/internodes.
  • Internodes ribbed, strengthened with silica.
  • Wedged microphylls alternate with branches in whorls.
  • Sporangia borne by sporangiophores in strobilus.
• Homosporous.
• Small bisexual gametophyte (green, free-living).
• Multiflagellated sperms.

Pterophyta (Ferns)

• Largest group (excluding flowering plants).
• Diverse in form and habit.
• Most familiar ferns: Filicales.
• Mostly homosporous.
• Sporophyte:
  • Siphonostelic rhizomes, mostly adventitious roots.
  • Leaves: Compound megaphylls (fronds).
  • Sporangia borne under leaf at margins or on stalks.
  • Sporangia in clusters called sori.
• Bisexual free-living gametophytes (prothallus), few subterranean.
• Gametophyte has rhizoids, short-lived.
• Multi-flagellated sperms.

Summary Table of Characteristics