Plant Classification Lecture

Introduction

• Over 400,000 species of plants on Earth.
• Plants differ in appearance, root systems, reproductive cycles, water transport.
• Use a classification system to group plants.
• Classification is based on observable characteristics.
• Evolution plays a key role in plant classification.

Early Plant Evolution

• Cyanobacteria (2.5 billion years ago):
  • First organisms to perform photosynthesis and release oxygen.
  • Not classified as plants.
• Algae:
  • Look similar to plants but are not true plants.
  • Three groups: brown, red, and green algae.
  • True plants share ancestors with green algae (chara orders).

Classification of Land Plants (Embryophytes)

• Divided into four major groups:
  1. Bryophytes
     • Oldest group (~470 million years ago).
     • Includes mosses, liverworts, hornworts.
     • Grow in moist habitats but not limited to them.
     • Lack true roots, have rhizoids.
     • Non-vascular, reproduce via spores.
  2. Pteridophytes
     • Includes ferns and lycophytes.
     • Have roots, stems, true leaves (fronds).
     • Vascular tissues allow growth taller than bryophytes.
     • Reproduce via spores.
  3. Gymnosperms
     • First seed plants (~350 million years ago).
     • Include conifers, cycads, ginkgo, and gnetophytes.
     • Naked seeds (ovules exposed in cones).
  4. Angiosperms
     • Youngest evolutionary group.
     • Seeds enclosed in fruits.
     • Bear flowers, make up 90% of all land plants.

Key Characteristics

• Non-Vascular Plants: Bryophytes
• Vascular Plants: Include pteridophytes, gymnosperms, and angiosperms.
• Seed Plants: Gymnosperms and angiosperms.
• Flowering Plants: Angiosperms.

Conclusion

• Land plants (embryophytes) are categorized into four groups based on vascular tissues and seed production.
• Angiosperms, known as flowering plants, are the largest and most diverse group.

Additional Information

• Additional videos available on bryophyte lifecycle and gymnosperm life cycle.