Chapter 3: Morphology of Flowering Plants

Introduction

Morphology refers to the study of form, structure, and various parts of plants and their arrangements. Plant morphology specifically examines the external features of plants, including roots, stems, leaves, flowers, fruits, and seeds. Understanding plant morphology is essential for plant identification, classification, and understanding plant adaptations and functions.

The Root System

Functions of Roots

• Anchorage: Hold the plant firmly in soil
• Absorption: Uptake of water and minerals
• Storage: Reserve food in modified roots
• Conduction: Transport water and nutrients to stem and leaves
• Vegetative propagation: Some modified roots can produce new plants

Types of Root Systems

Taproot System

• Primary root grows directly downward and remains dominant
• Secondary roots branch from the main taproot
• Characteristic of dicotyledonous plants
• Examples: Carrot, radish, mustard, mango

Fibrous Root System

• Primary root short-lived, replaced by numerous roots
• All roots are approximately equal in thickness
• Characteristic of monocotyledonous plants
• Examples: Grass, wheat, rice, maize

Modifications of Roots

Storage Roots

• Store food materials
• Examples:
  • Conical (carrot)
  • Fusiform (radish)
  • Napiform (turnip)
  • Tuberous (sweet potato)

Respiratory Roots (Pneumatophores)

• Grow vertically upward from the soil
• Contain specialized pores called pneumathodes
• Found in plants growing in swampy areas
• Example: Rhizophora, Avicennia

Prop Roots

• Provide additional support to the plant
• Arise from the aerial parts of the stem
• Examples: Banyan, screwpine (Pandanus)

Stilt Roots

• Provide support and anchorage
• Arise from the lower nodes of the stem
• Example: Maize, sugarcane

Buttress Roots

• Provide additional support to tall trees
• Board-like extensions at the base of the trunk
• Example: Silk cotton tree

The Shoot System

The Stem

Functions of Stem

• Provides support to branches, leaves, flowers, and fruits
• Conducts water, minerals, and photosynthates
• Produces leaves, branches, and flowers
• Performs photosynthesis (in green stems)
• Food storage in some modified stems

Modifications of Stem

Underground Stem Modifications

• Rhizome: Horizontal underground stem (ginger, turmeric)
• Tuber: Swollen tip of underground stem (potato)
• Bulb: Condensed stem with fleshy leaf bases (onion, garlic)
• Corm: Vertical underground stem (colocasia, gladiolus)

Sub-aerial Stem Modifications

• Runner: Horizontal stem growing above ground (grass, strawberry)
• Stolon: Horizontal branch arising from the base of stem (mint, jasmine)
• Offset: Short, thick runner (water hyacinth, pistia)
• Sucker: Underground branch that grows obliquely upward (chrysanthemum, banana)

Aerial Stem Modifications

• Tendrils: Thread-like climbing structures (grapevine, cucumber)
• Thorns: Sharp, pointed defensive structures (bougainvillea, citrus)
• Cladode: Flattened photosynthetic stem (opuntia)
• Phylloclade: Flattened green stem functioning as leaf (cactus)

The Leaf

Functions of Leaves

• Photosynthesis: Primary site of food production
• Transpiration: Loss of water as vapor
• Gaseous exchange: Intake of CO₂ and release of O₂
• Food storage in some modified leaves

Parts of a Typical Leaf

• Leaf base: Portion attached to the stem
• Petiole: Stalk connecting leaf blade to stem
• Lamina/Leaf blade: Expanded, flattened photosynthetic portion
• Stipules: Pair of appendages at leaf base (present in some plants)

Types of Leaves

Based on Arrangement of Leaves on Stem

• Alternate: One leaf at each node (sunflower, mustard)
• Opposite: Two leaves at each node (jamun, guava)
• Whorled: More than two leaves at each node (Alstonia)

Based on Composition of Leaf Blade

• Simple: Undivided leaf blade (mango, guava)
• Compound: Leaf blade divided into leaflets
  • Pinnately compound: Leaflets arranged along a central axis (neem, rose)
  • Palmately compound: Leaflets arranged radiating from a point (silk cotton)

Venation Patterns

• Reticulate (net-like): Characteristic of dicots (peepal, mango)
• Parallel: Characteristic of monocots (grass, banana)

Leaf Modifications

• Tendrils: For climbing (pea, glory lily)
• Spines: For defense and reducing water loss (cactus, opuntia)
• Phyllode: Flattened petiole functioning as leaf (Australian acacia)
• Storage leaves: Fleshy for water storage (aloe, agave)
• Insectivorous leaves: Modified to trap insects (pitcher plant, venus fly trap)

The Flower

Parts of a Flower

• Pedicel: Stalk of the flower
• Thalamus/Receptacle: Swollen end of the pedicel bearing floral parts
• Calyx: Outermost whorl composed of sepals
• Corolla: Second whorl composed of petals
• Androecium: Male reproductive part composed of stamens
• Gynoecium/Pistil: Female reproductive part composed of carpels

Androecium (Male Reproductive Part)

• Consists of stamens
• Each stamen has:
  • Filament: Stalk-like structure
  • Anther: Terminal portion containing pollen grains
• Types: Monadelphous, diadelphous, polyadelphous, syngenesious

Gynoecium (Female Reproductive Part)

• Consists of carpels (megasporophylls)
• Each carpel has:
  • Ovary: Basal swollen part containing ovules
  • Style: Elongated part connecting ovary and stigma
  • Stigma: Terminal receptive part for pollen

Types of Flowers

Based on Symmetry

• Actinomorphic: Radially symmetrical (mustard, datura)
• Zygomorphic: Bilaterally symmetrical (pea, bean)
• Asymmetric: No plane of symmetry (canna)

Based on Position of Ovary

• Hypogynous: Ovary superior (mustard, china rose)
• Perigynous: Ovary half-inferior (plum, rose)
• Epigynous: Ovary inferior (sunflower, cucumber)

Based on Number of Floral Parts

• Trimerous: Floral parts in multiples of three (lily)
• Tetramerous: Floral parts in multiples of four (mustard)
• Pentamerous: Floral parts in multiples of five (hibiscus)

Inflorescence

• Arrangement of flowers on the floral axis
• Types:
  • Racemose: Main axis continues to grow (mustard, radish)
  • Cymose: Main axis terminates in a flower (jasmine, cotton)
  • Special types: Spadix (colocasia), catkin (mulberry), head (sunflower)

Fruit

• Mature and ripened ovary developed after fertilization
• Functions: Protection and dispersal of seeds

Types of Fruits

Simple Fruits

• Developed from single ovary
• Types:
  • Dry dehiscent: Legume (pea), follicle (calotropis), capsule (cotton)
  • Dry indehiscent: Achene (sunflower), caryopsis (wheat), nut (cashew)
  • Fleshy: Berry (tomato), drupe (mango), pome (apple)

Aggregate Fruits

• Formed from multicarpellary apocarpous ovary
• Example: Raspberry, strawberry

Composite Fruits

• Developed from entire inflorescence
• Example: Pineapple, fig, mulberry

Seed

• Fertilized and mature ovule
• Contains embryo, stored food, and protective coat

Parts of a Seed

• Seed coat: Protective covering
• Cotyledons: Seed leaves storing food
• Embryonal axis: Develops into new plant
  • Radicle: Embryonic root
  • Plumule: Embryonic shoot

Types of Seeds

• Monocotyledonous: One cotyledon (maize, rice)
• Dicotyledonous: Two cotyledons (bean, pea)

Seed Dispersal

• Wind dispersal: Light seeds with wings or hair-like structures
• Water dispersal: Seeds with air spaces or waterproof coverings
• Animal dispersal: Hooks, spines, or edible fruits
• Explosive mechanism: Sudden release of seeds from dried fruits