🧠 Plant Morphology

This lesson covers external plant structures and modifications that are crucial for crop identification, propagation, and farm management.

Root Systems

Roots anchor plants, absorb water and minerals, and store food. There are two main root systems:

• Tap root system: A primary root grows vertically downward with secondary lateral branches. Found in most dicots (mustard, carrot, mango). Carrot, radish, and turnip are examples of modified tap roots that store food (fusiform, conical, and napiform modifications respectively).
• Fibrous root system: A cluster of thin, adventitious roots of similar size arising from the base of the stem. Found in monocots (rice, wheat, maize, grasses). This system is highly effective for soil binding and erosion prevention.

Modified roots include prop roots (banyan), stilt roots (maize, sugarcane), pneumatophores (mangrove breathing roots), and nodular roots (legumes with nitrogen-fixing Rhizobium bacteria, critical for soil fertility in agricultural rotations).

Stem Modifications

The stem supports leaves, flowers, and fruits while conducting water and nutrients. Stems show diverse modifications for specific functions:

• Underground stems: Rhizome (ginger, turmeric), tuber (potato), bulb (onion, garlic), and corm (colocasia, saffron) serve as storage organs and are used in vegetative propagation
• Sub-aerial stems: Runner (strawberry), stolon (mint), sucker (banana, chrysanthemum), and offset (water hyacinth) spread horizontally for propagation
• Aerial modifications: Tendrils (grapevine) for climbing, thorns (citrus, bougainvillea) for protection, and phylloclades (opuntia) for photosynthesis in arid conditions

Leaf Types and Modifications

Leaves are the primary photosynthetic organs. Based on the lamina (blade), leaves are classified as:

• Simple leaves: A single, undivided lamina (mango, hibiscus, banyan)
• Compound leaves: Lamina divided into leaflets. Pinnately compound (neem, rose) have leaflets arranged along a central rachis. Palmately compound (silk cotton) have leaflets radiating from a single point.

Leaf arrangement on the stem (phyllotaxy) can be alternate (mango), opposite (guava), or whorled (Alstonia). Leaf modifications include tendrils (pea), spines (cactus), storage leaves (onion scales), and insectivorous traps (pitcher plant, sundew).

Inflorescence

Inflorescence refers to the arrangement of flowers on the floral axis. Major types include:

• Racemose (indefinite): Main axis continues to grow. Examples: raceme (mustard), spike (wheat, amaranthus), panicle (rice, oat), corymb (candytuft), and umbel (coriander, carrot)
• Cymose (definite): Main axis terminates in a flower. Examples: monochasial cyme (jasmine) and dichasial cyme (Bougainvillea bract cluster)
• Special types: Capitulum/head (sunflower, marigold -- family Asteraceae), hypanthodium (fig), cyathium (Euphorbia), and verticillaster (tulsi, mint)

Understanding inflorescence types is important in crop identification, pollination management, and seed production in agriculture.

Summary Cheat Sheet

• Root systems: tap root (dicots) and fibrous root (monocots).
• Modified roots and stems support storage, support, survival, and propagation.
• Leaf forms and phyllotaxy aid crop identification and adaptation understanding.
• Inflorescence may be racemose, cymose, or specialized forms.
• Morphology knowledge supports agronomy, seed production, and breeding work.