Plant Diversity and Evolution Lecture Notes

Overview of Seed Plants

• Common examples: pines, palms, ginkgos, cycads, grasses, shrubs, deciduous trees, flowering plants.
• All are classified as seed plants.

Classification of Plants

1. Vascular Tissue

   • Non-vascular: Bryophytes (e.g., moss)
   • Vascular: Allows for larger growth through efficient material transport (xylem and phloem) and structural support.

2. Seeds vs. Spores

   • Spores: Discussed in spore-bearing or seedless vascular plants (e.g., ferns).
   • Seeds: Focus of current discussion.

Evolutionary Adaptations of Seed Plants

• Significance of Seeds:

  • Thick protective seed coat; withstands harsh conditions.
  • Contains embryo (baby plant) and nutritive tissue (provides energy).
  • Allows for a dormant stage, enabling survival in variable habitats.

• Significance of Pollen:

  • Male gametophyte; allows reproduction without water.
  • Can be transported by wind, water, or biotic vectors (e.g., bees).
  • Opens up a broader range of habitats compared to non-seed plants.

• Heterospory:

  • Contrasts with homospory (where all spores are alike).
  • Heterosporous plants produce:
    • Microspores: Develop into male gametophyte (pollen).
    • Megaspores: Develop into female gametophyte.
  • Female gametophyte produces eggs; male gametophyte produces sperm, leading to zygote formation.

Types of Seed Plants

• Gymnosperms: Non-flowering plants (e.g., conifers, cycads, ginkgos).
• Angiosperms: Flowering plants; produce seeds covered by fruit.

Angiosperms Subclassification

1. Monocots:

   • One cotyledon (embryonic leaf).
   • Flower parts in multiples of 3.
   • Parallel vein pattern in leaves.
   • Scattered vascular bundles in the stem.
   • Single pore in pollen grains.

2. Dicots:

   • Two cotyledons.
   • Flower parts in multiples of 4 or 5.
   • Net-like vein pattern in leaves.
   • Vascular bundles in a ring formation in the stem.
   • Three pores or furrows in pollen grains.

Conclusion

• Discussion on reproductive cycles of gymnosperms and angiosperms to follow in the next video.
• Questions can be left in the comments section.