Learning Objectives
- Understand the morphology of root, stem, leaf, flower, fruit, and seed
- Learn different types of root systems, stems, and leaf modifications
- Understand floral morphology and describe flowers using floral formula
- Study the structure of different types of fruits and seeds
Key Concepts
Root
Tap root system: Found in dicots. Primary root develops from radicle. Fibrous root system: Found in monocots. Primary root is short-lived, replaced by adventitious roots. Modifications: Storage roots (carrot — conical, radish — fusiform, sweet potato — tuberous), Pneumatophores (breathing roots in mangroves like Rhizophora), Stilt roots (maize), Prop roots (banyan), Nodular roots (legumes with Rhizobium).
Stem
Develops from plumule. Bears nodes, internodes, buds. Modifications: Underground stems (rhizome — ginger; tuber — potato; bulb — onion; corm — colocasia), Sub-aerial stems (runner — grass; stolon — strawberry; offset — water hyacinth; sucker — chrysanthemum), Aerial stems (tendril — grapevine; thorn — Bougainvillea; phylloclade — Opuntia; cladode — Asparagus).
Leaf
Parts: Leaf base (hypopodium), petiole (mesopodium), lamina (epipodium). Venation: Reticulate (dicots) or parallel (monocots). Types: Simple (undivided lamina) or Compound (divided into leaflets — pinnately compound like neem; palmately compound like silk cotton). Phyllotaxy: Alternate (sunflower), Opposite (Calotropis), Whorled (Alstonia). Modifications: Tendrils (pea), spines (cacti), pitcher (Nepenthes), bladder (Utricularia), phyllode (Australian Acacia).
Flower
A modified shoot for reproduction. Parts: Calyx (sepals — protective), Corolla (petals — attract pollinators), Androecium (stamens = filament + anther; male part), Gynoecium (carpels = stigma + style + ovary; female part). Placentation: Marginal (pea), Axile (hibiscus, tomato), Parietal (mustard), Free central (Dianthus), Basal (sunflower).
Aestivation: Arrangement of sepals/petals in bud. Valvate (Calotropis), Twisted (China rose), Imbricate (Cassia), Vexillary/Papilionaceous (pea).
Fruit and Seed
Fruit: Ripened ovary. True fruit develops from ovary alone. False fruit (pseudocarp) develops from other floral parts also (e.g., apple — thalamus). Seed: Contains seed coat (testa, tegmen), embryo (radicle, plumule, embryonal axis), and endosperm (food storage in endospermic seeds). Dicot seed: two cotyledons (e.g., gram). Monocot seed: one cotyledon + scutellum + coleoptile + coleorhiza (e.g., maize).
Description of Important Families
Fabaceae (Pea family): Papilionaceous corolla, diadelphous stamens (9+1), marginal placentation. Formula: % ⚥ K(5) C1+2+(2) A(9)+1 G1. Examples: pea, gram, soybean.
Solanaceae (Potato family): Epipetalous stamens, axile placentation, bicarpellary ovary. Formula: ⊕ ⚥ K(5) C(5) A5 G(2). Examples: tomato, potato, tobacco, petunia.
Liliaceae (Lily family): Perianth 6 (tepals), trimerous flower, axile placentation. Formula: ⊕ ⚥ P3+3 A3+3 G(3). Examples: lily, tulip, onion, garlic, Aloe.
Summary
Flowering plants have well-defined morphological structures. Roots, stems, and leaves undergo various modifications for special functions. Flowers are reproductive structures with four whorls. Fruits develop from ovaries after fertilization. Seeds contain the embryo for the next generation. Families Fabaceae, Solanaceae, and Liliaceae have characteristic floral features.
Important Terms
- Phyllotaxy: Arrangement of leaves on the stem
- Placentation: Arrangement of ovules within the ovary
- Aestivation: Arrangement of petals/sepals in a flower bud
- Pneumatophores: Breathing roots in mangrove plants
- Phylloclade: Flattened stem performing photosynthesis (e.g., Opuntia)
- Epipetalous: Stamens attached to petals
- Diadelphous: Stamens united in two bundles (9+1)
- Pseudocarp: False fruit developing from parts other than ovary
Quick Revision
- Tap root = dicots; Fibrous root = monocots
- Potato = stem tuber; Sweet potato = root tuber
- Onion = bulb (stem); Ginger = rhizome (stem)
- Reticulate venation = dicots; Parallel = monocots
- Fabaceae: papilionaceous, diadelphous, marginal placentation
- Solanaceae: epipetalous, bicarpellary, axile placentation
- Liliaceae: trimerous, perianth of tepals, axile placentation
- Apple = false fruit (thalamus); Mango = true fruit (ovary)