Quick Summary
Vegetative morphology studies the external form of roots, stems, and leaves — the vegetative organs. Understanding the modifications of each organ and their adaptive functions is the key to this chapter. Many modifications involve familiar plants, making them easier to learn with examples.
Root System
Types of Root Systems
| Type | Description | Example |
|---|---|---|
| Tap root system | Primary root + lateral branches | Mango, bean, sunflower (dicots) |
| Fibrous root system | Many equal roots from stem base | Rice, wheat, grass (monocots) |
| Adventitious roots | Arise from non-root parts | Banyan (prop roots), maize (stilt roots) |
Functions of Roots
- Absorption of water and minerals
- Anchorage
- Storage (modified roots)
Root Modifications
| Modification | Function | Example |
|---|---|---|
| Fusiform (tapering both ends) | Storage | Radish |
| Napiform (top-shaped) | Storage | Turnip |
| Conical (carrot-shaped) | Storage | Carrot |
| Tuberous (irregular) | Storage | Sweetpotato |
| Pneumatophore | Breathing in waterlogged soil | Rhizophora (mangroves) |
| Prop roots | Extra support | Banyan |
| Stilt roots | Support | Maize, Sugarcane |
| Parasitic (haustoria) | Absorb from host | Cuscuta |
Stem
Functions: Support, conduction, food storage, vegetative propagation.
Node: Point of leaf attachment. Internode: Region between nodes.
Underground Stem Modifications
| Modification | Features | Example |
|---|---|---|
| Rhizome | Horizontal, nodes and internodes visible | Ginger, turmeric |
| Corm | Solid, upright, fleshy | Colocasia, Gladiolus |
| Bulb | Fleshy leaves (scales) on a disc-shaped stem | Onion, garlic |
| Stem tuber | Terminal swelling of underground stem | Potato |
Aerial Stem Modifications
| Modification | Function | Example |
|---|---|---|
| Tendril | Climbing support | Passiflora (leaf tendril in pea) |
| Thorn | Protection | Citrus, Bougainvillea |
| Phylloclade | Photosynthesis (succulent, flattened) | Opuntia (cactus) |
| Bulbil | Vegetative reproduction | Agave, Dioscorea |
Sub-aerial Stem Modifications
| Type | Description | Example |
|---|---|---|
| Runner | Horizontal on ground, rooting at nodes | Grass, Oxalis |
| Stolon | Horizontal, arching | Jasmine |
| Offset | Short runner in aquatic plants | Pistia, Eichhornia |
| Sucker | Arises from underground stem base | Mint, Chrysanthemum |
Leaf
Parts of a Leaf: Leaf base, petiole (stalk), lamina (blade).
Simple leaf: Lamina in one piece (mango). Compound leaf: Lamina divided into leaflets — pinnate (neem) or palmate (silk cotton).
Venation
| Type | Description | Example |
|---|---|---|
| Reticulate | Network of veins | Dicots (mango, peepal) |
| Parallel | Veins run parallel | Monocots (banana, grass) |
Phyllotaxy
| Type | Leaves per node | Example |
|---|---|---|
| Alternate | 1 | Sunflower, mustard |
| Opposite | 2 | Calotropis, guava |
| Whorled | 3 or more | Nerium, Alstonia |
Leaf Modifications
| Modification | Function | Example |
|---|---|---|
| Tendril | Climbing support | Pea (leaflet tendril) |
| Spine | Protection | Opuntia, Aloe |
| Phyllode | Photosynthesis (petiole flattened) | Acacia melanoxylon |
| Pitcher | Insect trapping (nitrogen) | Nepenthes |
| Bladder | Aquatic insect trapping | Utricularia |
| Scale leaves | Protection of buds | Onion, ginger |
Worked Examples
Identify the modification: Potato — stem tuber (underground stem). Carrot — conical root. Onion — bulb. Pea tendril — leaf modification.
Phyllotaxy from diagram: Count nodes. One leaf per node → alternate. Two per node → opposite.
Important Questions
One Mark
- Name the type of root system in monocots.
- What is a phylloclade? Give one example.
- Define phyllotaxy.
- Which organ is modified to form a pitcher in Nepenthes?
Short Answer (3 marks)
- Distinguish between simple and compound leaves with one example each.
- Write any three modifications of tap roots with examples and functions.
- Compare alternate, opposite, and whorled phyllotaxy with one example each.
Long Answer (5 marks)
- Describe the underground modifications of stem with diagrams. Give one example for each type.
- Explain the different types of leaf modifications with function and example for each.
Common Mistakes
- Potato: students say it is a root modification — it is a stem tuber (has nodes, buds/"eyes").
- Sweet potato: it is a root modification (tuberous root) — opposite of potato.
- Pea tendril: it is a leaf modification (leaflet is modified), not a stem modification.
- Passiflora tendril: it is a stem modification.
Board Exam Tips
- Stem modification tables (underground, aerial, sub-aerial) appear as 5-mark questions with diagrams.
- "Identify and give the function" of a modification (e.g., Nepenthes, Opuntia, ginger) is common.
- Potato vs sweet potato is a famous trap question — know which is stem and which is root.
- NEET: Identification of modifications and phyllotaxy types appear regularly.
Frequently Asked Questions
Tap root: one main root with lateral branches; found in dicots (mango, bean). Fibrous root: many roots of similar thickness from the base of the stem; found in monocots (wheat, rice). Both absorb water and minerals.