Plant Diversity Lecture Notes

Introduction to Plant Diversity

• Overview of plant evolution and adaptation to land
• Discussion of various plant phyla and their characteristics

Early Life on Earth

• For the first 3 billion years, no life on land
• Cyanobacteria appeared around 1.2 billion years ago
• First plants, fungi, and animals colonized land around 500 million years ago

Evolutionary Relationship

• Land plants have terrestrial ancestors
• Close relatives: Green algae (charophytes)
• Shared traits with charophytes:
  • Rings of cellulose-synthesizing complexes
  • Peroxisome enzymes
  • Flagellated sperm
  • Formation of phragmoplast
• Land plants are called embryophytes (contain embryos)

Derived Traits of Land Plants

• Alternation of generations
• Multicellular, dependent embryos
• Walled spores in sporangia
• Multicellular gametangia
• Apical meristems

Benefits and Challenges of Land Colonization

• Benefits:
  • Abundant sunlight
  • Plenty of CO2
  • Rich, unused soil
  • Initially few herbivores or pathogens
• Challenges:
  • Water scarcity
  • Lack of structural support

Specific Adaptations

• Sporopollenin in spore walls (prevents desiccation)
• Development of cuticles
• Mycorrhizae (symbiotic relationships for nutrient uptake)

Fossil Evidence

• Plants on land for at least 475 million years
• Evolution timeline:
  • 475 million years ago: First land plants
  • 50 million years later: Vascular plants
  • 120 million years later: Gymnosperms and angiosperms

Plant Classification

• Nonvascular plants (bryophytes): Liverworts, mosses, hornworts
• Seedless vascular plants: Lycophytes, pterophytes
• Seed plants:
  • Gymnosperms: