Morphology in Flowering Plants

The Root

Overview

• Flowering plants, or angiosperms, have roots, stems, leaves, flowers, and fruits.
• Understanding these structures requires knowing standard terms and definitions.
• Plants adapt their structures for various purposes like protection, climbing, and storage.

Root System

• Types of Roots:
  • Tap Root System: Found in dicots; primary root with lateral roots (e.g., mustard plant).
  • Fibrous Root System: Found in monocots; many roots from the stem base (e.g., wheat plant).
  • Adventitious Roots: Arise from parts other than the radicle (e.g., grass, Monstera, banyan tree).
• Functions of Roots:
  • Absorption of water and minerals
  • Anchorage to the plant
  • Storage of food
  • Synthesis of growth regulators

Regions of the Root

• Root Cap: Protects the root tip.
• Region of Meristematic Activity: Small, thin-walled cells that divide repeatedly.
• Region of Elongation: Cells enlarge and elongate, contributing to root length.
• Region of Maturation: Cells differentiate and mature; root hairs form here, aiding in water and mineral absorption.

Modifications of Root

• Storage Roots: Tap roots (e.g., carrot, turnip) and adventitious roots (e.g., sweet potato) swell to store food.
• Prop Roots: Hanging roots from the banyan tree for support.
• Stilt Roots: Supportive roots from lower nodes of maize and sugarcane stems.
• Pneumatophores: Roots growing upwards in swampy areas (e.g., Rhizophora) to obtain oxygen for respiration.

The Stem

Features of the Stem

• Ascending part of the plant axis.
• Bears branches, leaves, flowers, and fruits.
• Develops from the plumule of a germinating seed.
• Contains nodes (where leaves are born) and internodes (space between nodes).
• Bears buds (terminal or axillary).
• Young stems are green; older stems become woody and dark brown.
• Main functions:
  • Spread out branches

• Conduct water, minerals, and photosynthates
• Storage of food
• Provide support and protection
• Aid in vegetative propagation

Modifications of Stem

• Storage:
  • Underground stems store food (e.g., potato, ginger, turmeric).
  • Act as organs of perennation to survive unfavorable conditions.
• Climbing:
  • Stem tendrils from axillary buds help plants climb (e.g., gourds, grapevines).
• Protection:
  • Axillary buds may become thorns (e.g., Citrus, Bougainvillea) to protect from animals.
• Photosynthesis:
  • Stems in arid plants like Opuntia and Euphorbia are flattened or fleshy and carry out photosynthesis.
• Spreading:
  • Underground stems of grass and strawberry spread to new areas.
  • In mint and jasmine, slender lateral branches grow and touch the ground to form new plants.
  • In aquatic plants like Pistia and Eichhornia, lateral branches with rosettes of leaves and roots form.
  • In banana, pineapple, and Chrysanthemum, lateral branches grow horizontally underground and rise obliquely upward to form leafy shoots.

The Leaf

Structure of a Leaf

• Lateral and generally flattened structure.
• Develops at the node and bears a bud in its axil.
• Leaves originate from shoot apical meristems.
• Main parts: leaf base, petiole, and lamina.
  • Leaf Base: Attaches the leaf to the stem and may have stipules.
  • Petiole: Holds the blade to light; long, flexible petioles allow fluttering in the wind.
  • Lamina: The green expanded part with veins and veinlets; has a midrib for rigidity and transport of materials.

Venation

• Reticulate Venation: Veinlets form a network (common in dicots).
• Parallel Venation: Veins run parallel (common in monocots).

Types of Leaves

• Simple Leaf: Lamina is entire or incised without touching the midrib.
• Compound Leaf: Lamina incisions reach the midrib, creating leaflets.
  • Pinnately Compound: Leaflets on a common axis (e.g., neem).
  • Palmately Compound: Leaflets attached at a common point (e.g., silk cotton).

Phyllotaxy

• Alternate: Single leaf at each node (e.g., china rose, mustard, sunflower).
• Opposite: Pair of leaves at each node, opposite to each other (e.g., Calotropis, guava).
• Whorled: More than two leaves arise at a node forming a whorl (e.g., Alstonia).

Modifications of Leaves

• Tendrils: For climbing (e.g., peas).
• Spines: For defense (e.g., cacti).
• Fleshy Leaves: For storing food (e.g., onion, garlic).
• Special Adaptations:
  • In Australian acacia, small and short-lived leaves with expanded petioles for photosynthesis.
  • In insectivorous plants like pitcher plant and Venus-fly trap, leaves are modified to trap insects.

The Inflorescence

Inflorescence

• Inflorescence: The arrangement of flowers on the floral axis.
• Types:
  • Racemose: Main axis keeps growing; flowers grow laterally in acropetal order (e.g., older flowers at the base).
  • Cymose: Main axis ends in a flower; flowers grow in basipetal order (e.g., older flowers at the top).

The Flower

• A Reproductive Unit: In angiosperms, meant for sexual reproduction.
• Parts of a Flower:
  • Thalamus/Receptacle: Swollen end of the stalk (pedicel) where floral parts are attached.
  • Whorls:
    • Calyx: Outer whorl, consists of sepals.
    • Corolla: Next whorl, consists of petals.
    • Androecium: Male reproductive part, consists of stamens.
    • Gynoecium: Female reproductive part, consists of carpels.
  • Perianth: When calyx and corolla are not distinct (e.g., lily).
• Types of Flowers:
  • Bisexual: Has both androecium and gynoecium.
  • Unisexual: Has either only stamens or only carpels.
• Symmetry:
  • Actinomorphic: Radial symmetry; can be divided into equal halves in any radial plane (e.g., mustard, datura).
  • Zygomorphic: Bilateral symmetry; can be divided into equal halves only in one plane (e.g., pea, gulmohur).
  • Asymmetric: Cannot be divided into equal halves in any plane (e.g., canna).
• Based on Floral Appendages:
  • Trimerous: Floral parts in multiples of 3.
  • Tetramerous: Floral parts in multiples of 4.
  • Pentamerous: Floral parts in multiples of 5.
• Bracts:
  • Bracteate: Flowers with bracts (reduced leaf at the base of the pedicel).
  • Ebracteate: Flowers without bracts.
• Position of Floral Parts:
  • Hypogynous: Gynoecium at the highest position; ovary is superior (e.g., mustard, china rose).
  • Perigynous: Gynoecium at the center; ovary is half-inferior (e.g., plum, rose).
  • Epigynous: Thalamus grows around the ovary; ovary is inferior (e.g., guava, cucumber).

Parts of a Flower

1. Calyx

• Calyx: The outermost whorl of the flower.
• Sepals: Members of the calyx, usually green and leaf-like.
• Function: Protects the flower in the bud stage.
• Types:
  • Gamosepalous: Sepals united.
  • Polysepalous: Sepals free.

2. Corolla

• Corolla: Composed of petals, usually brightly colored.
• Function: Attracts insects for pollination.
• Types:
  • Gamopetalous: Petals united.
  • Polypetalous: Petals free.
• Shapes: Tubular, bell-shaped, funnel-shaped, wheel-shaped.
• Aestivation: Arrangement of sepals or petals in the floral bud.
  • Valvate: Sepals or petals just touch each other (e.g., Calotropis).
  • Twisted: One margin overlaps the next one (e.g., china rose, lady’s finger).
  • Imbricate: Margins overlap in no specific direction (e.g., Cassia, gulmohur).
  • Vexillary: One large petal overlaps others (e.g., pea, bean).

3. Androecium

• Androecium: Male reproductive part.
• Stamen: Consists of a filament (stalk) and an anther.
• Anther: Usually bilobed with two pollen sacs where pollen grains are produced.
• Staminode: Sterile stamen.
• Attachment:
  • Epipetalous: Stamens attached to petals (e.g., brinjal).
  • Epiphyllous: Stamens attached to perianth (e.g., lily).
• Union Types:
  • Monoadelphous: Stamens united into one bundle (e.g., china rose).
  • Diadelphous: Stamens in two bundles (e.g., pea).
  • Polyadelphous: Stamens in more than two bundles (e.g., citrus).
• Length Variation: Different filament lengths within a flower (e.g., Salvia, mustard).

4. Gynoecium

• Gynoecium: Female reproductive part.
• Carpel: Consists of stigma, style, and ovary.
• Ovary: Enlarged basal part with one or more ovules.
• Style: Connects ovary to stigma.
• Stigma: Receptive surface for pollen grains.
• Types:
  • Apocarpous: Free carpels (e.g., lotus, rose).
  • Syncarpous: Fused carpels (e.g., mustard, tomato).
• Placentation: Arrangement of ovules within the ovary.
  • Marginal: Ovules along the ventral suture forming two rows (e.g., pea).
  • Axile: Ovules attached to the central axis in a multilocular ovary (e.g., china rose, tomato).
  • Parietal: Ovules on the inner wall or periphery of the ovary (e.g., mustard).
  • Free Central: Ovules on the central axis, no septa (e.g., Dianthus).
  • Basal: Single ovule at the base of the ovary (e.g., sunflower, marigold).

The Fruit

• Definition: A mature or ripened ovary of a flowering plant.
• Formation: Develops after fertilization.
  • Parthenocarpic Fruit: Formed without fertilization.
• Structure: Generally consists of a wall (pericarp) and seeds.
  • Pericarp: Can be dry or fleshy.
    • Thick and Fleshy Pericarp: Differentiated into three layers:
      • Epicarp: Outer layer.
      • Mesocarp: Middle layer.
      • Endocarp: Inner layer.
• Examples:
  • Mango: Differentiated pericarp with a thin epicarp, fleshy mesocarp, and hard endocarp.
  • Coconut: Fibrous mesocarp.

The Seed

• Definition: Develops from ovules after fertilization.
• Structure:
  • Seed Coat: Outer covering with two layers (testa and tegmen).
  • Embryo: Contains radicle, embryonal axis, and cotyledons.
    • Dicotyledonous Seeds: Two cotyledons (e.g., gram, pea).
    • Monocotyledonous Seeds: One cotyledon (e.g., wheat, maize).

Structure of a Dicotyledonous Seed

• Seed Coat: Two layers – outer testa and inner tegmen.
  • Hilum: Scar where seed was attached to the fruit.
  • Micropyle: Small pore above the hilum.
• Embryo: Contains embryonal axis and two cotyledons.
  • Radicle and Plumule: Present at the two ends of the embryonal axis.
• Endosperm: Food-storing tissue present in some seeds (e.g., castor).

Structure of a Monocotyledonous Seed

• Seed Coat: Membranous and fused with the fruit wall.
• Endosperm: Bulky and stores food.
  • Aleurone Layer: Proteinous layer separating endosperm and embryo.
• Embryo: Small, with one large cotyledon (scutellum).
  • Plumule and Radicle: Enclosed in sheaths called coleoptile and coleorhiza.

Semi-Technical Description of a Typical Flowering Plant

Introduction

• Description should be brief, simple, and scientific.
• Proper sequence: habit, vegetative characters (roots, stem, leaves), floral characters (inflorescence, flower parts).

Vegetative Characters

• Roots: Describe the type and characteristics.
• Stem: Note the structure and features.
• Leaves: Mention shape, arrangement, and other details.

Floral Characters

• Inflorescence: Type and description.
• Flower Parts: Detailed examination of each part.

Floral Diagram and Formula

• Floral Diagram:
  • Shows number, arrangement, and relation of flower parts.
  • Dot at the top represents the position of the mother axis.
  • Parts are drawn in whorls: calyx (outermost), corolla, androecium, gynoecium (center).
• Floral Formula Symbols:
  • Br: Bracteate
  • K: Calyx
  • C: Corolla
  • P: Perianth
  • A: Androecium
  • G: Gynoecium
  • G: Superior ovary
  • G: Inferior ovary
  • ♂: Male
  • ♀: Female
  • ⚥: Bisexual
  • ⊕: Actinomorphic (radial symmetry)
  • %: Zygomorphic (bilateral symmetry)
  • (): Fusion within parts
  • —: Adhesion between parts

Example: Mustard Plant (Family: Brassicaceae)

• Use floral diagram and formula to represent the mustard plant.
• Demonstrates cohesion and adhesion within and between whorls.

Important Plant Families

1. Fabaceae

• Also Known As: Papilionoideae, subfamily of Leguminosae
• Distribution: Worldwide

Vegetative Characters:

• Types: Trees, shrubs, herbs
• Roots: With root nodules
• Stem: Erect or climber
• Leaves: Alternate, pinnately compound or simple, with stipules; venation reticulate

Floral Characters:

• Inflorescence: Racemose
• Flower: Bisexual, zygomorphic
• Calyx: Five sepals, gamosepalous; valvate/imbricate aestivation
• Corolla: Five petals, polypetalous, papilionaceous (standard, wings, keel); vexillary aestivation
• Androecium: Ten stamens, diadelphous, dithecous anther
• Gynoecium: Superior ovary, monocarpellary, unilocular, many ovules; single style
• Fruit: Legume
• Seed: One to many, non-endospermic

Floral Formula: %(hermaphrodite symbol) K(5) C1+2+(2) A(9)+1 G1

Economic Importance:

• Pulses: Gram, arhar, sem, moong, soybean
• Edible oil: Soybean, groundnut
• Dye: Indigofera
• Fibres: Sunhemp
• Fodder: Sesbania, Trifolium
• Ornamentals: Lupin, sweet pea
• Medicine: Muliathi

2. Solanaceae

• Common Name: Potato family
• Distribution: Tropics, subtropics, temperate zones

Vegetative Characters:

• Types: Herbs, shrubs, rarely small trees
• Stem: Herbaceous or woody, aerial, branched, solid or hollow, hairy or glabrous; underground stem in potato
• Leaves: Alternate, simple or pinnately compound; venation reticulate

Floral Characters:

• Inflorescence: Solitary, axillary or cymose (as in Solanum)
• Flower: Bisexual, actinomorphic
• Calyx: Five sepals, united, persistent; valvate aestivation
• Corolla: Five petals, united; valvate aestivation
• Androecium: Five stamens, epipetalous
• Gynoecium: Bicarpellary, syncarpous; superior ovary, bilocular, many ovules; axile placentation
• Fruit: Berry or capsule
• Seed: Endospermous

Floral Formula: ⊕

Economic Importance:

• Food: Tomato, brinjal, potato
• Spice: Chilli
• Medicine: Belladonna, ashwagandha
• Fumigatory: Tobacco
• Ornamentals: Petunia

3. Liliaceae

• Common Name: Lily family
• Type: Monocotyledonous plants
• Distribution: Worldwide

Vegetative Characters:

• Types: Perennial herbs with bulbs, corms, or rhizomes
• Leaves: Mostly basal, alternate, linear, exstipulate; parallel venation

Floral Characters:

• Inflorescence: Solitary or cymose; often in umbellate clusters
• Flower: Bisexual, actinomorphic
• Perianth: Six tepals (3+3), often united into a tube; valvate aestivation
• Androecium: Six stamens (3+3), epitepalous
• Gynoecium: Tricarpellary, syncarpous; superior ovary, trilocular with many ovules; axile placentation
• Fruit: Capsule, rarely berry
• Seed: Endospermous

Floral Formula: Br ⊕ P(3+3) A3+3 G(3)

Economic Importance:

• Ornamentals: Tulip, Gloriosa
• Medicine: Aloe
• Vegetables: Asparagus
• Colchicine: Colchicum autumnale

Chapter Summary:

• Flowering plants show great variety in shape, size, structure, nutrition, life span, habit, and habitat.
• They have well-developed root and shoot systems.
• Root system types:
  • Tap root: Common in dicotyledonous plants.
  • Fibrous root: Common in monocotyledonous plants.
• Roots can be modified for:
  • Food storage
  • Mechanical support
  • Respiration
• Shoot system includes:
  • Stem
  • Leaves
  • Flowers
  • Fruits
• Stem features:
  • Presence of nodes and internodes
  • Multicellular hair
  • Positively phototropic nature
• Stems can be modified for:
  • Food storage
  • Vegetative propagation
  • Protection
• Leaf characteristics:
  • Lateral outgrowth from the stem at the node
  • Green color for photosynthesis
  • Variation in shape, size, margin, apex, and leaf blade (lamina) incisions
• Leaf modifications:
  • Tendrils for climbing
  • Spines for protection
• Flower:
  • Modified shoot for sexual reproduction
  • Arranged in different inflorescences
  • Varies in structure, symmetry, ovary position, and arrangement of petals, sepals, and ovules
• After fertilization:
  • Ovary becomes fruit
  • Ovules become seeds
• Seeds can be:
  • Monocotyledonous or dicotyledonous
  • Vary in shape, size, and viability period
• Floral characteristics help in classification and identification of flowering plants.
• Flowers are described using scientific terms in a specific sequence.
• Floral features are summarized as floral diagrams and floral formula.