Unit-I: Practical Study of Advanced Morphology

The objective of this unit is to gain practical knowledge about advanced morphology and the diversity of vegetative and reproductive structures in plants.

Phyllotaxy refers to the mode of arrangement of leaves on the stem or branch. The primary goal is to avoid overcrowding and ensure maximum exposure to sunlight.

Observations:

• Alternate: A single leaf arises at each node in an alternating manner (e.g., Hibiscus).
• Opposite: A pair of leaves arises at each node, standing opposite to each other.
  • Opposite Decussate: Successive pairs are at right angles (e.g., Calotropis).
  • Opposite Superimposed: Successive pairs are directly above one another (e.g., Guava).
• Whorled: More than two leaves arise at a single node forming a circle or whorl (e.g., Alstonia).

Leaves often undergo structural changes to perform specialized functions other than photosynthesis.

Common Practical Examples:

• Leaf Tendrils: The whole leaf or parts like leaflets are modified into sensitive, thread-like coils for climbing (e.g., Pisum sativum/Pea).
• Leaf Spines: Leaves or parts of leaves modified into sharp, pointed structures to reduce transpiration and provide protection (e.g., Opuntia, Aloe).
• Phyllode: The petiole becomes green, fleshy, and leaf-like to perform photosynthesis when the true lamina is reduced (e.g., Australian Acacia).
• Storage Leaves: Fleshy leaves that store food or water (e.g., Onion, Aloe).

Special inflorescences are condensed or highly modified arrangements that do not strictly follow typical racemose or cymose patterns.

Key Types to Identify:

• Cyathium: Characteristics include a cup-shaped involucre enclosing a single female flower and multiple male flowers (e.g., Euphorbia).
• Verticillaster: A cluster of sessile flowers forming a false whorl at the nodes (e.g., Ocimum/Tulsi).
• Hypanthodium: A fleshy, pear-shaped receptacle with an internal cavity housing small flowers (e.g., Ficus/Fig).

Practical Checklist

• Observe the phyllotaxy and note the leaf arrangement.
• Identify leaf modifications and state their functional significance.
• Examine special inflorescences using a hand lens to see minute floral parts.