Plant Diversity Notes

Plant Diversity Notes

Evolution of Plants

• Plants evolve and adapt to survive and compete.

• Development of new traits and abilities includes:

  • Vascular structures: Allow growth in height and facilitate nutrient transport.

  • Seeds: Provide protection and nourishment to the developing embryo.

  • Different life cycle stage dominance: Variation in which life cycle stage (gametophyte or sporophyte) is more dominant.

Plant Phylogenetic Tree

• Angiosperms:

  • Have seeds, flowers, and fruits.

  • Rapidly diversify and outnumber all other plant groups.

  • Utilize animals as pollinators for fertilization.

• Gymnosperms (e.g., Conifers):

  • Possess seeds and pollen grains.

  • Gametes dispersed by wind; can grow to incredible heights.

• Seedless Vascular Plants (e.g., Ferns):

  • Have vascular systems enabling taller growth.

  • Depend on water for gamete dispersal.

• Non-Vascular Plants (e.g., Mosses):

  • Cannot transport water via vascular tissue.

  • Depend on water to disperse gametes and were limited to aquatic habitats originally.

Alternation of Generations

• All plants alternate generations:

  • Gametophyte (haploid, n): Produces gametes.

  • Sporophyte (diploid, 2n): Produces spores.

• Different plant groups may spend varying amounts of time in each stage.

Nonvascular Plants

• Characteristics:

  • Lack vascular tissue.

  • Rely on water for gamete transport.

  • Gametophyte generation is dominant (n).

• Bryophyta (Mosses):

  • Spawn sporophyte that grows as stalks, producing spores.

• Hepaticophyta (Liverworts):

  • Also gametophyte dominant (n) with pores for gas exchange.

  • Use gemmae for asexual reproduction via gemma cups.

Seedless Vascular Plants

• Possess vascular tissue (xylem and phloem).

• Can grow taller than non-vascular plants, but still rely heavily on water for gamete dissemination.

• Sporophyte generation is dominant (2n).

• Major Groups:

  1. Lycophyta (Club Mosses):

  • Features strobili (cones) for spore production.

  1. Psilotophyta (Whisk Fern):

  • Sporophyte (2n) with sporangia on synangia.

  1. Sphenophyta (Horsetails):

  • Dominant sporophyte with strobili at stem tips.

  1. Pteridophyta (Ferns):

  • Dominant sporophyte with sporangia found in sori on leaf undersides.

Gymnosperms (Seed Plants)

• Composed of groups like Cycadophyta, Ginkgophyta, and Coniferphyta.

• Key Characteristics:

  • Vascular plants with seeds.

  • Sporophyte dominant (2n).

  • Protective seeds and pollen grains for reproductive cells.

  • Lack flowers; reproduce via cones (strobili).

• Cycadophyta (Cycads):

  • Large strobili; less prominent today.

• Ginkgophyta (Ginkgoes):

  • Only gymnosperm that cycles leaves with seasons; large seeds with fleshy seed coat.

• Coniferophyta (Conifers):

  • Includes many of the largest trees, such as Sequoias and pines; possess strobili.

Angiosperms (Flowering Plants)

• Evolved approximately 65 million years ago, characterized by:

  • Possession of flowers and fruit.

  • Most numerous plant group due to adaptations in reproduction (pollinators).

• Anthophyta (Flowering Plants):

  • Flowers consist of various structures including stamen (male) and carpels (female).

  • Seeds develop inside the ovary, which becomes the fruit once seeds begin to develop.