Morphology of Flowering Plants

When we talk about flowering plants, scientifically called angiosperms, we are essentially studying their external structure (morphology).

Despite the huge diversity—from tiny herbs to massive trees—all angiosperms share five basic organs:

• Root
• Stem
• Leaf
• Flower
• Fruit

Think of these as the fundamental building blocks of plant life.

🌱 The Root System

Functions of Roots

Roots are not just “underground parts”—they are highly active organs:

• Absorb water and minerals
• Provide anchorage
• Store food
• Produce growth hormones

Types of Root Systems

1. Tap Root System (Dicots)

• Develops from the radicle (embryonic root)
• Has a primary root → secondary → tertiary roots
• Example: Mustard, Tomato

👉 Concept: Deep penetration → strong anchorage

2. Fibrous Root System (Monocots)

• Primary root is short-lived
• Replaced by many thin roots at the base of stem
• Example: Wheat, lettuce

👉 Concept: Surface spread → prevents soil erosion

3. Adventitious Roots

• Arise from parts other than radicle
• Example: Banyan, grass, monstera, strawberry

👉 Concept: Functional adaptation beyond normal roots

Regions of Root

Imagine root as a growing machine with specialized zones:

Region	Function
Root cap	Protection
Meristematic region	Cell division
Elongation zone	Growth in length
Maturation zone	Differentiation + root hairs

👉 Root hairs are crucial because they increase absorption surface area.

Root Modifications

Roots can change their structure for survival advantages:

• Storage → carrot, turnip, sweet potato
• Support → banyan (prop roots), maize (stilt roots)
• Respiration → pneumatophores in swamp plants like Rhizophora

👉 This shows an important concept:
Structure changes according to function (Adaptation).

🌿 The Stem

The stem develops from the plumule and grows upwards.

Key roles:

• Supports leaves, flowers, fruits
• Conducts water and nutrients
• Produces buds
• Helps in vegetative propagation

Key Structural Terms

• Node → point where leaf arises
• Internode → space between two nodes

👉 This distinction is often asked in prelims.

Stem Modifications

Stems can be modified to perform special functions

Types	Function	Example	Key Feature / Note
Underground Stems	Store food and help the plant survive harsh conditions	Potato	Stem grows below ground and accumulates nutrients
Thorns	Protection from herbivores	Bougainvillea	Stem modified into sharp spine
Propagation (Runners/Stolons)	Formation of new plants	Strawberry	Spreading underground stems give rise to new plants
Stem Tendrils	Climbing support	Pumpkin	Thin, coiled structures; axillary bud modified into tendril
Photosynthetic Stems	Perform photosynthesis in arid conditions	Euphorbia	Fleshy, cylindrical green stems carry out photosynthesis
Lateral Branches	Help in vegetative propagation (forming new plants)	Mint	Branches develop roots and grow into new plants

🍃 The Leaf

Leaves are the food factories of the plant due to photosynthesis.

Parts of a Leaf

Part	Function
Leaf base	Attaches leaf to stem
Petiole	Holds leaf for sunlight
Lamina	Main photosynthetic surface

👉 The lamina contains veins and veinlets for transport and support

Venation (Pattern of Veins)

• Reticulate venation → network (dicots)
• Parallel venation → parallel lines (monocots)

👉 This is a classic monocot vs dicot differentiator.

Types of Leaves

1. Simple Leaf: Lamina not fully divided

2. Compound Leaf: Lamina divided into leaflets

Types of Compound Leaves:

• Pinnate → arranged along rachis (neem)
• Palmate → from one point (silk cotton)

👉 Key concept:
Leaflets do NOT have buds, but leaves do.

Phyllotaxy (Leaf Arrangement)

Type	Pattern	Example
Alternate	One leaf per node	Mustard
Opposite	Two leaves per node	Guava
Whorled	More than two leaves	Alstonia

👉 Helps in maximum sunlight exposure.

Leaf Modifications

Leaves also adapt:

• Tendrils → climbing (pea)
• Spines → protection (cactus)
• Storage → onion, garlic
• Photosynthesis via petiole → Australian acacia
• Insectivorous leaves → pitcher plant, Venus flytrap

🌸 The Flower — A Modified Shoot

The most important idea to start with:

👉 A flower is not a separate entity, it is actually a modified shoot.

• The shoot apical meristem transforms into a floral meristem
• Growth becomes compact
• Instead of leaves, it produces floral organs

👉 Conceptually:
Vegetative phase → Reproductive phase transition

🌼 Structure of a Flower

All floral parts are arranged on a swollen base called:
👉 Thalamus (Receptacle)

Four Main Whorls

Whorl	Nature	Function
Calyx	Accessory	Protection
Corolla	Accessory	Attraction
Androecium	Reproductive	Male part
Gynoecium	Reproductive	Female part

👉 If calyx and corolla are not distinct → Perianth (e.g., lily)

🌿 Calyx (Sepals)

• Outermost whorl
• Usually green and leaf-like
• Protects the flower bud

Types:

• Gamosepalous → fused sepals
• Polysepalous → free sepals

🌺 Corolla (Petals)

• Brightly coloured → attract pollinators
• Shapes vary: tubular, bell-shaped, funnel-shaped

Types:

• Gamopetalous → fused petals
• Polypetalous → free petals

🔁 Aestivation (Arrangement in Bud)

Aestivation is the arrangement of sepals or petals in a flower bud in relation to each other.

Type	Pattern	Example
Valvate	Edges touch, no overlap	Calotropis
Twisted	Overlapping in sequence	China rose
Imbricate	Irregular overlap	Cassia
Vexillary	Special papilionaceous pattern	Pea

👉 Helps in taxonomic identification

♂️ Androecium (Male Reproductive Part)

Made of stamens.

Structure of Stamen

• Filament → stalk
• Anther → produces pollen

👉 Pollen grains = male gametophyte

Variations in Stamens

Based on attachment:

• Epipetalous → attached to petals (brinjal)
• Epiphyllous → attached to perianth (lily)

Based on fusion:

• Polyandrous → free
• Monadelphous → one bundle
• Diadelphous → two bundles
• Polyadelphous → many bundles

👉 These are very important for plant classification questions.

♀️ Gynoecium (Female Reproductive Part)

Made of carpels.

Structure of Carpel

Part	Function
Stigma	Receives pollen
Style	Connects stigma to ovary
Ovary	Contains ovules

👉 Ovules later become seeds

Types Based on Carpels

• Apocarpous → free carpels (lotus)
• Syncarpous → fused carpels (mustard)

Placentation (Arrangement of Ovules)

This tells us how ovules are arranged inside ovary.

Type	Description	Example
Marginal	Along edge	Pea
Axile	Central axis	Tomato
Parietal	Inner wall	Mustard
Basal	Base	Sunflower
Free central	Central without septa	Marigold

🌸 Classification of Flowers

Based on Reproductive Parts

• Bisexual → both androecium + gynoecium
• Unisexual → only one

Based on Symmetry

Type	Meaning	Example
Actinomorphic	Radial symmetry	Mustard
Zygomorphic	Bilateral symmetry	Pea
Asymmetric	No symmetry	Canna

Based on Number of Floral Parts

• Trimerous → multiples of 3 (monocots)
• Tetramerous → multiples of 4
• Pentamerous → multiples of 5

Based on Ovary Position

Type	Ovary Position	Example
Hypogynous	Superior ovary	Mustard
Perigynous	Half inferior	Rose
Epigynous	Inferior ovary	Guava

👉 Shortcut:

• Hypo = below → ovary above
• Epi = above → ovary below

🌼 Inflorescence (Arrangement of Flowers on a stem)

Types:

1. Racemose

• Main axis keeps growing
• Flowers in acropetal order (old → base)

2. Cymose

• Main axis stops growing
• Flowers in basipetal order (old → top)

👉 This reflects growth pattern differences.

🍎 The Fruit

👉 A fruit is a mature ovary after fertilisation → Contains seeds + pericarp

Special case: Parthenocarpic fruit → develops without fertilisation (e.g., banana)

Structure of Fruit Wall (Pericarp)

Layer	Function
Epicarp	Outer
Mesocarp	Middle (often edible)
Endocarp	Inner

Example: Drupe

• Hard endocarp (stone fruit)
• Example: Mango, coconut

🌱 The Seed

👉 Seed = mature ovule after fertilisation

Parts of Seed

Part	Function
Seed coat	Protection
Embryo	Future plant

Embryo Components

• Radicle → future root
• Embryonal axis → future shoot
• Cotyledons → food storage

Monocot vs Dicot Seed

Feature	Monocotyledonous Seed	Dicotyledonous Seed
Number of Cotyledons	One	Two
Examples	Wheat, maize, rice, lily, grass	Bean, pea, gram, mango, sunflower
Seed Coat	May be distinct or fused with the fruit wall	Two distinct layers
Venation in Leaves	Parallel	Reticulate (net-like)
Flower Parts	Usually in multiples of three	Usually in multiples of four or five
Root System	Adventitious and fibrous	Taproot
Vascular Bundles	Scattered in the stem	Arranged in a ring
Pollen Structure	Single furrow or pore	Three furrows or pores