Morphology in Flowering Plants

The Root

Overview

• Flowering plants (angiosperms) have roots, stems, leaves, flowers, and fruits.
• Understanding these structures/organs requires knowing standard terms and definitions.
• Plant morphology is the study of the form and external features of above mentioned plant organs.
• The underground part of a flowering plant forms the root system, while the above-ground part constitutes the shoot system.
• Plants modify their organs for various purposes like support, protection, climbing, and storage.

Root System

In most plants, the root develops from the radicle of the embryo.

• Types of Roots:
  • Tap Root System: Found in dicots.
    • Formed by elongation of the radicle
    • Consists of a primary root with secondary and tertiary lateral roots
    • Example: Mustard
  • Fibrous Root System: Found in monocots.
    • Primary root is short-lived and replaced by many roots arising from the base of the stem
    • Example: Wheat
  • Adventitious Roots:
    • Arise from plant parts other than the radicle.
    • Example: Grass, Monstera, Banyan
• Functions of Roots:
  • Absorption of water and minerals from the soil
  • Anchorage of the plant
  • Storage of reserve food
  • Synthesis of some plant growth regulators

Regions of the Root

1. Root Cap (Calyptra)
   • Thimble-like protective structure at the root tip
   • Protects the tender growing apex as it penetrates soil
   • Absent in epiphytes, parasites, hydrophytes and mycorrhizal roots
2. Region of Meristematic Activity
   • Located just above the root cap
   • Cells are small, thin-walled, with dense protoplasm
   • Actively divide
3. Region of Elongation
   • Cells undergo rapid elongation and enlargement
   • Responsible for increase in root length
4. Region of Maturation (Differentiation)
   • Cells differentiate into permanent tissues
   • Root hairs develop from epidermal cells
   • Root hairs absorb water and minerals
   • Root hairs absent in mycorrhizal roots
5. Region of Mature Cells
   • Cells no longer divide or elongate
   • Impermeable to water
   • Helps in firm anchorage

Modifications of Root

Roots may modify to perform functions other than absorption and conduction.

1. Storage Roots: Tap roots (e.g., carrot, turnip) and adventitious roots (e.g., sweet potato, Asparagus) swell to store food.
2. Prop Roots: Hanging roots that provide support (e.g., Banyan tree)
3. Stilt Roots: Supportive roots arising from lower nodes of stem (e.g., maize and sugarcane).
4. Pneumatophores (Breathing Roots):
   • Vertical, upward-growing roots in swampy areas
   • Help in respiration by absorbing oxygen
   • Example: Rhizophora, Sonneratia (mangroves)

The Stem

Features of the Stem

Stem develops from the plumule of the embryo.

• Ascending part of the plant axis.
• Bears branches, leaves, flowers, and fruits.
• Develops from the plumule of a germinating seed.
• Contains nodes (points where leaves arise/born) and internodes (region between 2 nodes).
• Bears buds (which may be terminal or axillary).
• Young stems are green; older stems often become woody and dark brown.

“A bud is a compact, undeveloped young shoot with a growing point covered by young leaves”.
Largest bud example: Cabbage.

Functions of the Stem

• Bears and spreads branches with leaves, flowers and fruits
• Conducts water, minerals and photosynthates
• Stores food in some plants
• Provides support and protection
• Aids 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.
  • “Underground stem of potato is called a tuber and also helps in vegetative propagation.”
  • “Rhizome is a horizontally growing underground stem with nodes, internodes, scaly leaves and buds (e.g., ginger, turmeric).”
  • “Corm is a short, vertical, swollen underground stem that stores food and aids vegetative reproduction (e.g., Colocasia, Amorphophallus).”
• Climbing:
  • “Stem tendrils are slender, spirally coiled structures arising from axillary buds.”
  • e.g., gourds, grapevines.
• Protection:
  • “Thorns are modified stem structures containing vascular tissue and protect plants from grazing.”
  • Axillary buds become thorns.
  • e.g., Citrus, Bougainvillea.
• Photosynthesis:
  • Stems in arid plants become flattened or fleshy and carry out photosynthesis.
  • e.g., Opuntia and Euphorbia.
  • “Such photosynthetic stem modifications are called phylloclades.“
  • “A single-internode, leaf-like photosynthetic stem is called a cladode (e.g., Ruscus, Asparagus).”
• Spreading:
  • Underground stems of grass and strawberry spread to new areas.
    • “Such spreading underground stems are called runners.”
  • In mint and jasmine, slender lateral branches grow and touch the ground to form new plants.
    • “This type of stem modification is called stolon.”
  • In aquatic plants like Pistia and Eichhornia, lateral branches with rosettes of leaves and roots form.
    • “This modification is called offset.”
  • In banana, pineapple, and Chrysanthemum, lateral branches grow horizontally underground and rise obliquely upward to form leafy shoots.
    • “These underground lateral branches are called suckers.”

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.
    • “In monocots, the leaf base often forms a sheath that partially or completely encloses the stem.”
    • “In some legumes, the leaf base becomes swollen and is called pulvinus.”
  • Petiole: Holds the blade to light.
    • Long, flexible petioles allow fluttering in wind.
    • “Petiole helps in cooling the leaf and facilitating gaseous exchange.”
  • Lamina: The green expanded part with veins and veinlets.
    • Has a midrib for rigidity and transport of materials.
    • “Veins provide mechanical strength and act as channels for transport of water, minerals and food.”

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 arranged on a common axis (e.g., neem).
  • Palmately Compound: Leaflets attached at a common point (e.g., silk cotton).

“A bud is present in the axil of the petiole in both simple and compound leaves, but not in leaflets.”

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 carry out 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:
  1. Racemose: Main axis keeps growing.
     • Flowers grow laterally in acropetal order (i.e., older flowers at the base).
     • “Racemose inflorescence may be simple (unbranched axis) or compound (branched axis).”
     • “Examples of simple racemose: raceme (Delphinium), spike (Achyranthes), corymb (Iberis), umbel (Prunus), capitulum (sunflower), spadix (Colocasia), catkin (Populus).”
     • “Examples of compound racemose: panicle (Delonix), compound umbel (coriander), compound spike (wheat), compound spadix (coconut), compound capitulum (Echinops).”
  2. Cymose: Main axis ends in a flower.
     • Flowers grow in basipetal order (i.e., older flowers at the top).
     • “Cymose inflorescence shows limited growth.”
     • “Uniparous (monochasial): peduncle produces one lateral branch at a time (helicoid – Drosera; scorpioid – Heliotropium).”
     • “Biparous (dichasial): peduncle produces two lateral branches (e.g., jasmine, teak).”
     • “Multiparous (polychasial): more than two lateral branches arise (e.g., Calotropis).”

• Special Types of Inflorescence
  • “Hypanthodium: hollow, fleshy receptacle with an apical opening (e.g., Ficus species).“
  • “Verticillaster: condensed dichasial cyme appearing as whorls (e.g., Ocimum).“
  • “Cyathium: cup-shaped involucre enclosing one female and many male flowers (e.g., Euphorbia).“

The Flower

“A flower is a modified shoot in which the shoot apical meristem changes into a floral meristem.”

• A Reproductive Unit: In angiosperms, meant for sexual reproduction.
• Parts of a Flower:
  1. Thalamus/Receptacle: Swollen end of the stalk (pedicel) where floral parts are attached.
  2. Whorls:
     1. Calyx: Outer whorl, consists of sepals.
     2. Corolla: Next whorl, consists of petals.
     3. Androecium: Male reproductive part, consists of stamens.
     4. Gynoecium: Female reproductive part, consists of carpels.
        • “Flowers having all four whorls are complete; those lacking any whorl are incomplete.”
  3. Perianth: When calyx and corolla are not distinct (e.g., lily).

“Calyx and corolla are accessory (non-essential) organs, while androecium and gynoecium are reproductive organs.”

• Types of Flowers:
  1. Bisexual: Has both androecium and gynoecium.
  2. 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:
  1. Gamopetalous: Petals united.
  2. Polypetalous: Petals free.
• Shapes: Tubular, bell-shaped, funnel-shaped, wheel-shaped.
• Aestivation: Arrangement of sepals or petals in the floral bud.
  1. Valvate: Sepals or petals just touch each other without overlapping (e.g., Calotropis).
  2. Twisted: One margin overlaps the next in regular manner (e.g., china rose, lady’s finger).
  3. Imbricate: Margins overlap irregularly, not in any definite order (e.g., Cassia, gulmohur).
  4. Vexillary: One large petal overlaps the others (e.g., pea, bean).
  5. “Quincuncial: Out of five petals, two are completely external, two completely internal and one is partly internal and partly external.”

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 without pollen grains.
• Attachment:
  • Epipetalous: Stamens attached to petals (e.g., brinjal).
  • Epiphyllous: Stamens attached to perianth (e.g., lily).
  • “Gynandrous: Stamens attached to gynoecium (e.g., Calotropis).“
• Union Types (Cohesion of Stamens):
  • Monoadelphous: Stamens united into one bundle (e.g., china rose).
  • Diadelphous: Stamens united into two bundles (e.g., pea).
  • Polyadelphous: Stamens in more than two bundles (e.g., citrus).
  • “Syngenesious: Stamens united by anther lobes but filaments free (e.g., sunflower family).“
  • “Synandrous: Stamens united by both anthers and filaments (e.g., cucurbits).“
• Length Variation of Stamens: Different filament lengths within a flower (e.g., Salvia, mustard).
  • “Didynamous: Four stamens arranged as two long and two short (e.g., Lamiaceae family).“
  • “Tetradynamous: Six stamens arranged as four long and two short (e.g., mustard family).“

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: Carpels free (e.g., lotus, rose).
  • Syncarpous: Carpels fused (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, without septa (e.g., Dianthus).
  • Basal: Single ovule at the base of the ovary (e.g., sunflower, marigold).

“Superficial placentation: Ovules borne on placentae spread over inner surface of ovary walls (e.g., Nymphaea).“

The Fruit

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

“Mango and coconut are examples of drupe fruits.“

Classification of Fruits

• “Simple fruits: Develop from monocarpellary or multicarpellary syncarpous ovary.“

Dry fruits:
• “Dehiscent: Pea (pod), Delphinium (follicle), mustard (siliqua), cotton (capsule).“
• “Indehiscent: Maize (caryopsis), marigold (cypsela), litchi (nut).“
• “Schizocarpic: Castor (regma), coriander (cremocarp), Acacia (lomentum).“

Fleshy fruits:
• “Drupe (mango), Berry (tomato), Pepo (cucumber), Pome (pear), Hesperidium (orange), Balausta (pomegranate).”

Aggregate fruits:
• “Develop from multicarpellary apocarpous ovary (e.g., strawberry, custard apple).“

Composite fruits:
• “Develop from complete inflorescence: Sorosis (pineapple) and Syconus (banyan).“

The Seed

• Definition: Seed 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).

“In seeds like gram, pea and bean, endosperm is absent at maturity and such seeds are called non-endospermic.”

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.

“Most monocot seeds are endospermic, except some like orchids.”

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 whorl).

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:
  • “A symbolic representation summarising all important floral characters.”
• Floral Formula Symbols:
  • Br: Bracteate
  • K: Calyx
  • C: Corolla
  • P: Perianth
  • A: Androecium
  • G: Gynoecium
  • G̲: Superior ovary
  • Ḡ: Inferior ovary
  • ♂: Male
  • ♀: Female
  • ⚥: Bisexual
  • ⊕: Actinomorphic (radial symmetry)
  • %: Zygomorphic (bilateral symmetry)
  • (): Fusion within parts
  • —: Adhesion between parts

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; reticulate venation.

Floral Characters:

• Inflorescence: Racemose
• Flower: Bisexual, zygomorphic
• Calyx: 5 sepals, gamosepalous; valvate/imbricate aestivation
• Corolla: 5 petals, polypetalous, papilionaceous (standard, wings, keel); vexillary aestivation
• Androecium: 10 stamens, diadelphous, dithecous anther
• Gynoecium: Superior ovary, monocarpellary, unilocular, many ovules; single style
• Fruit: Legume
• Seed: One to many, non-endospermic

Floral Formula: % ⚥ 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; reticulate venation.

Floral Characters:

• Inflorescence: Solitary, axillary or cymose (as in Solanum)
• Flower: Bisexual, actinomorphic
• Calyx: 5 sepals, united, persistent; valvate aestivation
• Corolla: 5 petals, united; valvate aestivation
• Androecium: 5 stamens, epipetalous
• Gynoecium: Bicarpellary, syncarpous; superior ovary, bilocular, many ovules; axile placentation
• Fruit: Berry or capsule
• Seed: Endospermous

Floral Formula: ⊕ ⚥ K(5) C(5) A5 G(2)

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: 6 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 of roots:
• 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 hairs
• Positively phototropic nature

Stem modifications help in:
• Food storage
• Vegetative propagation
• Protection

Leaf

Characteristics:
• Lateral outgrowth from the stem at the node
• Green in colour due to chlorophyll for photosynthesis
• Shows variation in shape, size, margin, apex and lamina (leaf blade) incisions

Leaf modifications include:
• Tendrils for climbing
• Spines for protection
• “Fleshy leaves for food storage and special leaves for insect capture.”

Flower

• Modified shoot meant for sexual reproduction
• Arranged in different types of inflorescences
• Varies in structure, symmetry, ovary position, and arrangement of sepals, petals and ovules

After Fertilization

• Ovary develops into fruit
• Ovules develop into seeds

Seeds may be:
• Monocotyledonous or dicotyledonous
• Variable in shape, size and viability period

Taxonomic Importance

• Floral characteristics help in classification and identification of flowering plants
• Flowers are described using scientific terms in a fixed sequence
• “Floral features are represented concisely using floral diagrams and floral formulae.”