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Morphology of Flowering Plants

Jul 29, 2024

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.