Study Notes on Morphology of Flowering Plants

Biology: Morphology of Flowering Plants

01. INTRODUCTION

  • Angiosperms (flowering plants) exhibit significant diversity in their external structure or morphology.
  • Key structures in angiosperms include:
    • Roots
    • Stems
    • Leaves
    • Flowers
    • Fruits
    • Seeds
  • Two main systems of flowering plants:
    • Root System: Underground part comprising the primary root and its branches (secondary, tertiary roots).
    • Shoot System: Above-ground part encompassing stem, leaves, flowers, and fruits.

02. THE ROOT

  • Roots demonstrate specific growth patterns:
    • Geotropic: (+) negatively or positively away/toward gravity.
    • Hydrotropic: (+) positively towards water.
    • Phototropic: (-) negatively away from light.
1. TYPES OF ROOTS

  • (A) Tap Roots:

    • Characteristic of most dicot plants.
    • The primary root arises from the elongation of the radicle and bears secondary and tertiary roots.
    • Example: Mustard Plant.

  • (B) Adventitious Roots:

    • Develop from parts of the plant other than the radicle.
    • Example: Grass, Monstera, Banyan tree.

  • (C) Fibrous Roots:

    • Found in monocots where the primary root is short-lived.
    • These roots originate from the base of the stem.
    • Example: Wheat Plant.
Functions of Root System
  • Absorption of water and minerals.
  • Anchoring the plant in the soil.
  • Storage of reserve food materials.
  • Synthesis of plant growth regulators.
2. MODIFICATIONS OF ROOTS
(A) Modifications of Tap Root:
  1. Food Storage: Examples include Radish, Carrot, Turnip, and Sugar Beet.
  2. Nitrogen Fixation: Nodulated roots are formed with bacteria like Rhizobium in species such as Pea, Gram, and Beans (family Fabaceae).
  3. Respiration: Pneumatophores, observed in Rhizophora, are roots that grow vertically for oxygen absorption.
(B) Modifications of Adventitious Roots:
  1. Storage of Food: Examples include Asparagus, Dahlia, and Sweet Potato (Ipomoea batatas).
  2. Support:
    • (a) Stilt Roots: Supports from lower nodes (e.g., Maize, Sugarcanes).
    • (b) Prop Roots: Hang down from branches (e.g., Banyan Tree).
    • (c) Climbing Roots: Support for climbing plants (e.g., Money Plant, Monstera).

03. THE STEM

  • Developed from the plumule of the embryo during germination, the stem contains nodes and internodes.
  • Functions include:
    • Support and space for leaves, flowers, and fruits.
    • Conduction of water, minerals, and photosynthates (food).
    • Storage of food (examples: Potato, Ginger, Turmeric).
1. MODIFICATIONS OF STEMS
  • Sub-aerial: Partly aerial and partly underground (e.g., Runner, Stolon, Sucker, Offset).
  • Underground: Entirely below soil (e.g., Rhizome, Tuber, Corm, Bulb).
  • Aerial: Above ground (e.g., Stem Thorn, Stem Tendril, Phylloclade, Cladode).
Regions of the Root-tip
  • Root Hair: Absorbs water and minerals.
  • Root Cap: Protects the root apex.
  • Region of Elongation: Growth of root length.
  • Region of Meristematic Activity: Site of cell division.
Sub-aerial Modification of Stem Examples:
  • Runner: Develops roots below and leaves above (e.g., Strawberry).
  • Stolon: A lateral branch that arches down to the ground (e.g., Jasmine).
  • Sucker: Horizontally growing branches that emerge upward (e.g., Mint).
  • Offset: Short lateral branch with roots and leaves (e.g., Aquatic plants like Pistia, Eichhornia).
Underground Modification of Stem Examples:
  • Tuber: Swollen stem (eyes) for food storage (e.g., Potato).
  • Bulb: Reduced stem with fleshy leaves (e.g., Onion).
Aerial Modification of Stem Examples:
  • Stem Tendril: Helps in climbing (e.g., Grapevine).
  • Stem Thorn: Protection mechanism (e.g., Bougainvillea).
  • Phylloclade: Flattened stem for photosynthesis (e.g., Opuntia).

04. THE LEAF

  • Leaves develop from nodes and are pivotal for photosynthesis. Main structures include:
    1. Leaf Base: Attachment point to stem.
    2. Petiole: Stalk connecting leaf to the stem (absent in sessile leaves).
Leaf Structure and Functions
  • The leaf lamina primarily functions in photosynthesis, gas exchange, and transpiration.
  • Leaf venation:
    • (A) Reticulate: Common in dicots.
    • (B) Parallel: Found in monocots.
Types of Leaves
  • (A) Simple Leaf: Entire or incised lamina, not up to the midrib.
  • (B) Compound Leaf: Lamina divided into leaflets (two types: Pinnately compound and Palmately compound).
Phyllotaxy (Arrangement of Leaves)
  • Alternate: One leaf at each node (e.g., Mustard).
  • Opposite: Pair of leaves at each node (e.g., Guava).
  • Whorled: More than two leaves at each node (e.g., Alstonia).
Modifications of Leaves
  • Examples:
    1. Leaf Tendrils: For climbing (e.g., Pea).
    2. Leaf Pitcher: Modified lamina as a pitcher (e.g., Nepenthes).
    3. Fleshy Leaves: For food storage (e.g., Onion).
    4. Leaf Spines: Protection (e.g., Opuntia).

05. THE INFLORESCENCE

  • Inflorescence is the arrangement of flowers on the floral axis.
  • Two main types:
    • Racemose: Unrestricted growth of the floral axis, flowers arranged acropetally.
    • Cymose: Limited growth with flowers arranged basipetally.
Types of Racemose Inflorescence
  • Raceme: Flowers borne on elongated peduncle (e.g., Mustard).
  • Spike: Elongated peduncle with sessile flowers (e.g., Grass family).
  • Catkin: Thin peduncle with unisexual flowers (e.g., Oak).
  • Spadix: Thick, fleshy peduncle with small flowers covered by bracts (e.g., Maize).
  • Capitulum: Inflorescence with small sessile flowers arranged on a receptacle (e.g., Sunflower).
Types of Cymose Inflorescence
  • Main axis terminates in a flower; characterized by a basal arrangement.
Special Types of Inflorescence
  • Hypanthodium: Contains male, female, and sterile flowers together (e.g., Banyan).

06. THE FLOWER

  • The flower is a modified shoot where the apical meristem converts to floral meristem. It consists of:
    • Calyx: Outer whorl of sepals.
    • Corolla: Whorl of petals.
    • Androecium: Male reproductive part (stamens).
    • Gynoecium: Female reproductive part (carpels).
Floral Structures and Functions
  • Flowers may be classified based on their completeness:
    • Complete Flower: All four floral whorls present.
    • Incomplete Flower: One whorl is absent.
    • Bisexual Flower: Both reproductive organs present.
    • Unisexual Flower: One reproductive organ present.
Floral Symmetry
  • (A) Actinomorphic: Can be divided into equal halves (e.g., Mustard).
  • (B) Zygomorphic: Can be divided into equal halves through a specific plane (e.g., Pea).
  • (C) Asymmetrical: Cannot be divided into equal halves (e.g., Canna).
Position of Floral Parts
  • (A) Hypogynous: Gynoecium at the top; ovary superior (e.g., Mustard).
  • (B) Perigynous: Ovary in a cup structure; half inferior (e.g., Rose).
  • (C) Epigynous: Ovary enclosed; ovary inferior (e.g., Guava).

07. THE FRUIT

  • Fruits develop from mature ovaries post-fertilization.
  • Key components include:
    • Pericarp: Wall of the fruit with three layers:
    • Epicarp: Outermost layer.
    • Mesocarp: Middle, often fleshy layer.
    • Endocarp: Innermost layer.
Types of Fruits
  1. True Fruit: Develops solely from the ovary.
  2. False Fruit: Develops from ovary plus other parts (e.g., Strawberry).
  3. Simple Fruits: Develop from one ovary, can be fleshy or dry.
  4. Aggregate Fruits: Develop from multiple carpels (e.g., Raspberry).
  5. Composite Fruits: Formed from a cluster of flowers (e.g., Pineapple).
  6. Dry Fruits: Include capsules and pods (e.g., Pea, Mustard).

08. THE SEED

  • Seeds form from fertilized ovules, containing:
    • Seed coat
    • Embryo: Comprising cotyledons, radicle, and plumule.
Structure of Dicot and Monocot Seeds
  • Dicot: Generally contains two cotyledons, large and fleshy for food reserves.
  • Monocot: Usually has one cotyledon (scutellum), with bulky endosperm; contains embryonic structures covered by sheaths.

09. SEMI-TECHNICAL DESCRIPTION

  • It involves documenting morphological features of flowering plants including habit, vegetative, floral characters, and presenting them using a floral diagram and formula.

10. DESCRIPTION OF SOME IMPORTANT FAMILIES

CRUCIFERAE (Mustard Family)
  • Floral characters include:
    • Inflorescence: Typical raceme.
    • Ebracteate biological features with bisexual flowers, typically actinomorphic.
    • Calyx: 4 sepals, imbricate aestivation.
    • Corolla: 4 petals, cruciform.
    • Androecium: 6 stamens, tetradynamous condition.
    • Gynoecium: Bicarpellary, syncarpous, unilocular ovary becoming bilocular due to false septum.
    • Fruit: usually siliqua.
MALVACEAE (Cotton Family)
  • Inflorescence: Solitary or cymose.
  • Floral features: Bracteate, bisexual flowers, hypogynous.
  • Fruit: Capsule (e.g., ladyfinger, cotton).
FABACEAE (Pea Family)
  • Inflorescence: Typical raceme.
  • Gynoecium: Monocarpellary, unilocular.
  • Fruit: Legume or pod, non-endospermic seeds.
SOLANACEAE (Potato Family)
  • Inflorescence: Solitary or cymose.
  • Gynoecium: Bicarpellary, syncarpous.
  • Fruit: Berry, non-endospermic seeds.
ASTERACEAE (Sunflower Family)
  • Characterized by capitulum.
  • Petals 5, gamopetalous.
  • Fruits are cypsela with hairy pappus for fruit dispersal.
GRAMINEAE (Grass Family)
  • Inflorescence: Spikelets.
  • Gynoecium: Monocarpellary; fruit is caryopsis.
LILIACEAE (Lily Family)
  • Inflorescence: Solitary or cymose.
  • Floral characters: Monocot with no distinction between calyx and corolla.
Economic Importance
  • Various families discussed have significant agricultural, medicinal, and ornamental value.