Angiosperm Evolution and Diversity Notes

Basal Angiosperms and Phylogeny

• Basal Angiosperms:
  • ANA grade: Refers to Amborella, Nymphaea, and Austrobaileyales.
  • Characterized by flowers, carpels, double fertilization, and endosperm.
  • Evolved around 145 million years ago, diversified by 65 million years ago.

Angiosperm Evolution

• Divergence: Angiosperms and gymnosperms diverged approximately 305 million years ago.
  • Bennettitales: Extinct seed plants with flower-like structures, possibly related to angiosperms.
• Fossil Angiosperms:
  • Chinese fossils (125 million years old) show traits of modern angiosperms but lack some features.
  • Archaefructus sinensis has anthers and carpels but lacks petals and sepals.

Angiosperm Classification

• Paraphyletic Group: "Basal" angiosperms form a paraphyletic group.
  • Grade: United by anatomical and physiological traits, not strictly by phylogeny.
• APG IV Classification: Major clades include:
  • Rosids
  • Asterids
  • Eudicots
  • Monocots

Key Angiosperm Characteristics

• ANITA Grade: Includes Amborella, Nymphaeales, and Austrobaileyales.
• Unique Traits:
  • Carpel, endosperm, reduced gametophytes.
  • Vessels in wood and ethereal oils in some groups.
  • Tricolpate pollen in some lineages.

Amborella trichopoda

• Significance: New Caledonia is a biodiversity hotspot, preserving ancient Gondwanan flora.
  • Amborella trichopoda is a primitive plant found there, offering insights into early angiosperm evolution.

Nymphaeaceae (Water Lily Family)

• Habit: Aquatic, rhizomatous herbs.
  • Leaves: Large, alternate, simple, long-petiolate with floating blades.
  • Flowers: Solitary, large, bisexual, radial, with long pedicels.

Austrobaileyales

• Examples: Star anise (Illicium verum), Magnolia vine, Schisandra glabra.
  Economic importance: Nymphaea (water-lilies) are commonly used in garden pools.