Morphology of Flowering Plants - Lecture Notes

Introduction

• Discussing the morphology (external structure and appearance) of angiosperms (flowering plants).
• Angiosperms are characterized by flowers, enclosed seeds, and double fertilization.

Basic Features of Angiosperms

1. Presence of Flowers: The visible flowers are the primary characteristic.
2. Enclosed Seeds: Seeds are not naked; they are enclosed within fruits.
3. Double Fertilization: Two male gametes are released; one fuses with the female gamete to form a zygote (fertilization), and the other fuses with polar nuclei to form a triploid endosperm.

Morphology Overview

• Parts Studied: Root, stem, leaf, flower, fruit, seed.
• Adaptations: Each part may have multiple functions and can modify itself for different roles (e.g., roots for water absorption, anchorage, storage).

Root System

• Types of Roots:

  • Tap Root: One primary root with secondary and tertiary roots (e.g., mustard). Found in dicots and gymnosperms.
  • Fibrous Root: Multiple roots arising from the base of the stem (e.g., wheat). Found in monocots.
  • Adventitious Root: Roots arising from non-radical parts (e.g., banyan tree).

• Functions of Roots:

  • Water and mineral absorption
  • Anchorage
  • Storage
  • Synthesis of plant growth regulators (e.g., auxins and cytokinins)

• Modified Roots:

  • For storage (e.g., carrot, sweet potato)
  • For support (e.g., prop roots in banyan)
  • For respiration (e.g., pneumatophores in Rhizophora)

Stem

• Functions:

  • Conduction of water, minerals, and food
  • Storage
  • Support
  • Protection

• Structure:

  • Ascending part of the plant, usually above ground
  • Nodes (where leaves/branches arise) and internodes (segments between nodes)
  • Bearing buds that can develop into branches

• Modified Stems:

  • For storage (e.g., potato, ginger)
  • For support (e.g., tendrils in gourds)
  • For protection (e.g., thorns in citrus)
  • For photosynthesis (e.g., phylloclades in cacti)

Leaf

• Parts of a Leaf:

  • Leaf Base: Attaches the leaf to the stem, may bear stipules
  • Petiole: The stalk that connects the leaf blade to the leaf base
  • Lamina (Leaf Blade): The broad, flat part for photosynthesis

• Types of Venation:

  • Parallel Venation: Veins run parallel, typical in monocots
  • Reticulate Venation: Network of veins, typical in dicots

• Types of Leaves:

  • Simple Leaf: A single, undivided blade
  • Compound Leaf: Leaf blade divided into leaflets
    • Pinnately compound (e.g., neem)
    • Palmately compound (e.g., silk cotton)

• Phyllotaxy:

  • Arrangement of leaves on a stem
  • Alternate: Single leaf at each node alternately
  • Opposite: Pair of leaves at each node
  • Whorled: More than two leaves at each node

• Leaf Modifications:

  • For support (e.g., tendrils in peas)
  • For protection (e.g., spines in cacti)
  • For storage (e.g., succulent leaves)
  • For trapping insects (e.g., pitcher plant)

Inflorescence

• Arrangement of flowers on a floral axis
• Types:
  • Racemose: Oldest flowers at the base, youngest at the tip
  • Cymose: Oldest flowers at the tip, growth is determinate

The Flower

• Structure:

  • Pedicel: Stalk of the flower
  • Thalamus (Receptacle): Enlarged part where floral whorls arise
  • Calyx (Sepals): Outer whorl, green
  • Corolla (Petals): Colorful whorl
  • Androecium (Stamens): Male reproductive part
  • Gynoecium (Carpels/Pistil): Female reproductive part

• Floral Formula: Symbolic representation of flower structure

Aestivation

• Arrangement of sepals and petals in the bud
• Types:
  • Valvate: Sepals/petals touch but do not overlap (e.g., Calotropis)
  • Twisted: One edge overlaps the next one (e.g., China Rose)
  • Imbricate: Overlapping in an irregular manner
  • Vexillary: Five petals - standard, wings, keel (e.g., pea)

Placentation

• Arrangement of ovules within the ovary
• Types:
  • Marginal: Ovules along the margin (e.g., pea)
  • Axile: Ovules on the central axis (e.g., tomato)
  • Parietal: Ovules on the periphery (e.g., mustard)
  • Free Central: Ovules on a central column (e.g., primrose)
  • Basal: Ovules at the base (e.g., sunflower)

Fruit and Seed

• Fruit: Mature ovary

  • Pericarp: Wall of the fruit, may be differentiated into epicarp, mesocarp, and endocarp
  • Types of Fruits: Drupe (e.g., mango, coconut)

• Seed: Mature ovule

  • Parts:
    • Seed Coat: Protective outer layer
    • Embryo: Develops into a new plant (includes cotyledons, plumule, radicle)

• Types of Seeds:

  • Dicot: Two cotyledons (e.g., gram, pea)
  • Monocot: One cotyledon (e.g., maize)

Plant Families

Brassicaceae (Mustard Family)

• Floral Formula:
  • K2+2 C4 A2+4 G(2)
• Examples: Brassica (mustard)

Fabaceae (Pea Family)

• Floral Formula:
  • K(5) C1+2+(2) A(9)+1 G1
• Examples: Pea, gram, soyabean

Solanaceae (Potato Family)

• Floral Formula:
  • K(5) C(5) A(5) G(2)
• Examples: Potato, tobacco, tomato

Conclusion

• Detailed study of the morphology of flowering plants including roots, stems, leaves, flowers, fruits, seeds, and plant families.
• Understanding external adaptations and structures of various plant parts aids in identifying and classifying flowering plants.