Plant Diversity

Evolution of Plants

• Plants evolve and adapt to survive, developing new traits like vascular structures and seeds.

Plant Phylogenetic Tree

• Non-Vascular Plants (e.g., Mosses):
  • First to invade terrestrial habitats.
  • Algal ancestors.
  • Dependent on water for gamete dispersal.
• Seedless Vascular Plants (e.g., Ferns):
  • Have a vascular system, allowing taller growth.
  • Still depend on water for gamete dispersal.
• Gymnosperms (e.g., Conifers):
  • Have seeds and pollen grains.
  • Gametes dispersed by wind.
• Angiosperms:
  • Have seeds, flowers, and fruits.
  • Use animals for pollination, leading to rapid diversification.

Alternation of Generations

• All plants have two multicellular generations:
  • Gametophyte (haploid) produces gametes.
  • Sporophyte (diploid) produces spores.

Nonvascular Plants

• Lack vascular tissue and rely on water for gamete transport.
• Gametophyte dominant (n).

Hepaticophyta (Liverworts)

• Gametophyte dominant (n).
• Have pores for gas exchange and gemma cups for asexual reproduction.

Bryophyta (Mosses)

• Gametophyte dominant (n).
• Sporophytes grow as stalks that produce spores.

Seedless Vascular Plants

• Have vascular tissue (xylem and phloem) for true roots, stems, and leaves.
• Sporophyte generation is dominant.

Lycophyta (Club Mosses)

• Sporophyte dominant (2n).
• Vascular tissue allows upright growth.
• Possess strobili (cones) that produce spores.

Psilotophyta (Whisk Fern)

• Sporophyte dominant (2n).
• Sporangia are located on synangia.

Sphenophyta (Horsetails)

• Sporophyte dominant (2n).
• Strobili (cones) are found at the tips of stems.

Pteridophyta (Ferns)

• Sporophyte dominant (2n).
• Sporangia are in sori on the underside of leaves, sometimes covered by an indusium.

Gymnosperms (Seed Plants)

• Vascular plants with seeds; sporophyte dominant (2n).
• Seeds and pollen protect reproductive cells.
• Have secondary growth (wood and bark).
• Have strobili (cones) instead of flowers.

Cycadophyta (Cycads)

• Have large strobili (male: long, female: round).
• Pollen grains are found in the cones.

Ginkgophyta (Ginkgoes)

• Only gymnosperm to cycle leaves seasonally.
• Produces large seeds with a fleshy seed coat.

Coniferophyta (Conifers)

• Includes pines, firs, cypresses, junipers, and redwoods.
• Have strobili (cones).

Angiosperms (Flowering Plants)

• Seed plants with flowers and fruit.
• Most recent group to evolve.
• Flowers and fruit allow for vast range expansion.
• Pollen grains are mostly dispersed by pollinators.

Anthophyta (Flowering Plants)

• Flowers have stamen and carpels (male and female structures).
• Seeds develop within the ovary, which becomes the fruit.