Morphology is the external structure and features of flowering plants. CBSE Class 11 dedicates a full chapter to it. NEET asks direct questions on modifications, inflorescence types and floral formulas.
Core Concepts
Root system
Tap root (dicots) with primary root and branches; fibrous (monocots) from the stem base; adventitious (from non-root parts, like mango cuttings). Functions — anchorage, water and mineral absorption, storage.
How to identify root vs stem underground: Roots lack nodes, internodes, buds, and leaves. Stems have all four. A potato tuber has “eyes” (buds at nodes) — clearly a stem. A sweet potato has no nodes — clearly a root.
Root modifications
Tap root modifications — fusiform (radish), napiform (turnip), conical (carrot). Adventitious modifications — tuberous (sweet potato), fasciculated (dahlia), nodulose (mango ginger), prop (banyan), stilt (maize).
| Modification | Type | Example | Function |
|---|---|---|---|
| Fusiform | Tap root, swollen in middle | Radish | Food storage |
| Napiform | Tap root, swollen at top | Turnip, beetroot | Food storage |
| Conical | Tap root, gradually tapers | Carrot | Food storage |
| Tuberous | Adventitious, no definite shape | Sweet potato | Food storage |
| Prop/Pillar | Adventitious, from branches | Banyan | Support |
| Stilt | Adventitious, from lower nodes | Maize, sugarcane | Support |
| Pneumatophore | Adventitious, grows upward | Rhizophora (mangrove) | Aeration |
| Nodular | On legume roots | Pea, soybean | Nitrogen fixation (Rhizobium) |
Stem
Main axis. Modifications — underground (rhizome in ginger, tuber in potato, bulb in onion, corm in colocasia), sub-aerial (runner, stolon, sucker, offset), aerial (tendril, thorn, phylloclade in Opuntia).
Underground stem modifications:
| Type | Example | Identifying features |
|---|---|---|
| Rhizome | Ginger, turmeric | Horizontal, nodes with scale leaves |
| Tuber | Potato | Swollen tip of underground stolon, eyes (buds) at nodes |
| Bulb | Onion, garlic | Fleshy scale leaves around short disc-like stem |
| Corm | Colocasia, saffron | Vertical, solid, nodes with buds |
Sub-aerial stem modifications (vegetative reproduction):
- Runner: Creeps along soil surface, rooting at nodes (lawn grass, Oxalis)
- Stolon: Arches over ground, roots at tip (strawberry, jasmine)
- Sucker: Underground lateral branch that surfaces away from parent (banana, chrysanthemum)
- Offset: Short thick lateral branch in aquatic plants (water hyacinth, Pistia)
Aerial stem modifications:
- Tendril: Coiled, climbing organ (grape vine — stem tendril; pea — leaf tendril)
- Thorn: Hard, pointed (Bougainvillea — stem thorn; Argemone — leaf thorn)
- Phylloclade: Flattened stem performing photosynthesis (Opuntia — the “leaves” are actually flattened stems; true leaves are reduced to spines)
NEET frequently asks: “Is potato a root or stem?” (stem — has eyes/buds at nodes). “Is ginger a root?” (no — it is a rhizome/underground stem with nodes and scale leaves). “What type of modification is Opuntia?” (phylloclade — flattened stem).
Leaf
Three parts — leaf base, petiole, lamina. Venation — reticulate (dicot) or parallel (monocot). Types — simple (one lamina) or compound (pinnate or palmate). Phyllotaxy — alternate, opposite or whorled.
Leaf modifications:
- Tendrils: For climbing (pea — leaflets modified into tendrils)
- Spines: For protection and water conservation (cactus — leaves modified into spines)
- Storage leaves: Fleshy for food/water storage (onion — fleshy scale leaves)
- Pitcher: For insect capture (Nepenthes — leaf forms a pitcher trap)
- Bladder: For insect capture underwater (Utricularia — bladder traps on leaves)
Inflorescence
Arrangement of flowers on the flower axis. Racemose — main axis continues, flowers open from base upward (mustard). Cymose — main axis ends in a flower (Jasminum). Special — cyathium (Euphorbia), hypanthodium (fig).
Racemose types: Raceme (mustard), spike (Amaranthus), spadix (banana), umbel (coriander), capitulum/head (sunflower — the “flower” is actually many tiny flowers arranged in a disc).
Cymose types: Monochasial (one branch), dichasial (two branches — Jasminum), polychasial (multiple branches).
Special inflorescences:
- Cyathium (Euphorbia): One female flower surrounded by male flowers, all enclosed by an involucre of bracts that looks like a single flower
- Hypanthodium (Ficus/fig): Flask-shaped receptacle containing hundreds of tiny flowers inside — the fig is actually a hollow inflorescence
Flower structure
A complete flower has four whorls: calyx (sepals), corolla (petals), androecium (stamens), gynoecium (carpels). Bisexual flowers have both stamens and carpels; unisexual have only one.
Floral formula notation: Example for Brassicaceae (mustard family):
Where = actinomorphic, K = calyx, C = corolla, A = androecium, G = gynoecium. Parentheses around G indicate fused carpels (syncarpous). A line above G means superior ovary; below means inferior.
Fruit types
True fruits develop from ovary only. False fruits include non-ovarian tissue (apple). Simple — one ovary (mango drupe, pea legume). Aggregate — many ovaries of one flower (strawberry). Composite — whole inflorescence becomes a fruit (jackfruit, pineapple).
| Type | Example | Developed from |
|---|---|---|
| Drupe | Mango, coconut | Single ovary, stony endocarp |
| Berry | Tomato, grape | Single ovary, fleshy pericarp |
| Legume | Pea, bean | Single ovary, dehiscent |
| Capsule | Cotton, poppy | Multi-carpellary, dehiscent |
| False fruit (pome) | Apple | Thalamus + ovary |
| False fruit (syconus) | Fig | Entire inflorescence (hypanthodium) |
Worked Examples
Potato has nodes (eyes) and buds — stem features. Sweet potato has no nodes and develops from a root — adventitious root modification.
Monocot — one cotyledon, fibrous roots, parallel venation, flower parts in threes. Dicot — two cotyledons, tap root, reticulate venation, flower parts in fours or fives.
The flat green structures of Opuntia are not leaves — they are flattened stems (phylloclades) that perform photosynthesis. The true leaves are reduced to spines for water conservation. Evidence: phylloclades bear flowers, fruits, and areoles (buds with spines) — only stems do this.
Common Mistakes
Calling ginger a root. It is an underground stem (rhizome) with nodes and scale leaves.
Confusing racemose and cymose. Racemose has an indefinite main axis; cymose is definite.
Saying all fruits come from the ovary. False fruits include other parts.
Confusing stem tendrils and leaf tendrils. In grape vine, the tendril is a modified stem. In pea, the tendril is a modified leaflet. The origin determines the type.
Thinking the sunflower “flower” is one flower. It is a capitulum inflorescence — the outer “petals” are ray florets and the centre consists of hundreds of disc florets.
Exam Weightage and Revision
NEET 2023 tested the modification type of potato. NEET 2022 asked about types of inflorescence. CBSE boards ask five-mark questions on root/stem modifications with examples. Morphology gives 2-3 NEET questions per year — all factual recall.
When a question gives a scenario, identify the core mechanism first, then match it to the concepts above. Most wrong answers come from reading the scenario too quickly.
Memorise one example per modification type — that alone answers NEET direct questions on morphology.
Practice Questions
Q1. Is onion a stem or a root? Justify.
Onion is a stem modification (bulb). The fleshy part consists of modified leaves (scale leaves) that store food. At the base is a short, disc-like stem from which adventitious roots grow downward. The presence of a stem disc with nodes and fleshy leaves confirms it is a stem, not a root.
Q2. Differentiate between racemose and cymose inflorescence.
In racemose, the main axis continues to grow indefinitely (indeterminate), and flowers open from the base upward (centripetal). In cymose, the main axis terminates in a flower (determinate), and flowers open from top downward (centrifugal). Example: mustard (racemose), jasmine (cymose).
Q3. What is a pneumatophore? Give an example.
A pneumatophore is an aerial root that grows upward from waterlogged soil. It has lenticels (pores) for gas exchange — essentially a breathing root. Found in mangrove plants like Rhizophora and Avicennia that grow in oxygen-poor swamp soils.
Q4. Classify mango fruit and explain its structure.
Mango is a drupe (a simple fleshy fruit). Structure: Epicarp (thin outer skin), Mesocarp (fleshy edible part), Endocarp (hard stony layer enclosing the seed). Other drupes: coconut, peach, cherry, plum.
Q5. Why is apple called a false fruit?
In apple, the fleshy edible part develops from the thalamus (receptacle), not from the ovary wall. The true fruit (developed from ovary) is the core containing seeds. Since non-ovarian tissue forms the main edible part, apple is a false fruit (pseudocarp). Similarly, strawberry’s fleshy part is the swollen thalamus — the actual fruits are the tiny “seeds” on the surface (achenes).
FAQs
What is the difference between a thorn and a spine? A thorn is a modified stem (has vascular tissue, arises from axil of leaf). Example: Bougainvillea. A spine is a modified leaf or stipule (no vascular tissue of stem origin). Example: cactus spines. Both are sharp and protective, but their origin differs.
How do you tell if an underground structure is a root or stem? Check for nodes and internodes, buds, and scale leaves. If present, it is a stem (ginger, potato, onion). If absent, it is a root (carrot, sweet potato). Roots also lack the ability to produce leaves or flowers.
What is the largest flower in the world? Rafflesia arnoldii — a parasitic plant from Southeast Asia. Its flower can be 1 metre across and weigh 10 kg. It has no leaves, stem, or roots — it grows entirely inside its host plant and only emerges to produce its enormous foul-smelling flower.
Morphology rewards observation. Pick up any plant and you can classify most of its parts using the categories above.