Chapter 5: Morphology of Flowering Plants | Summary

The stem is the ascending part of the plant axis, developing from the plumule of the embryo. It bears nodes (where leaves are attached) and internodes (portions between nodes), and carries terminal or axillary buds. Stems are generally green when young but become woody and dark brown with age. They are distinguished from roots by features such as nodes and internodes, multicellular hairs, and positive phototropism.

The primary function of the stem is to spread branches bearing leaves, flowers, and fruits, and to conduct water, minerals, and photosynthates. Stems in some plants are modified for food storage (e.g., potato), support (e.g., tendrils), protection (e.g., thorns), or vegetative propagation (e.g., runners). These modifications represent adaptive strategies to different environments.

The leaf is a lateral, flattened structure borne on the stem at the node, with an axillary bud in its axil. A typical leaf has three parts: leaf base (which attaches to the stem and may bear stipules), petiole (which holds the lamina to light), and lamina (the green, expanded blade with veins). In monocots, the leaf base expands into a sheath; in some legumes it forms a swollen pulvinus. Veins provide rigidity and serve as transport channels for water, minerals, and food.

Venation — the arrangement of veins in the lamina — is reticulate (network-like) in dicots and parallel in most monocots. Leaves are classified as simple (lamina entire or incisions not reaching midrib) or compound (incisions reach midrib, forming leaflets). Compound leaves may be pinnately compound (leaflets on a rachis, e.g., neem) or palmately compound (leaflets at tip of petiole, e.g., silk cotton). Phyllotaxy — the pattern of leaf arrangement on the stem — may be alternate (one leaf per node), opposite (two leaves per node), or whorled (more than two leaves per node).

A flower is a modified shoot where the shoot apical meristem transforms into a floral meristem, internodes do not elongate, and the axis becomes condensed. Floral appendages are produced laterally instead of leaves. The arrangement of flowers on the floral axis is called inflorescence. Two major types are recognised based on whether the apex produces a flower or continues to grow.

In racemose inflorescences, the main axis continues to grow and flowers are borne laterally in acropetal succession (older flowers at base, younger toward apex). In cymose inflorescences, the main axis terminates in a flower, limiting its growth, and flowers are borne in basipetal order (older flowers at the top). These two types represent fundamentally different developmental patterns of floral arrangement.

The flower is the reproductive unit of angiosperms, borne on a pedicel with a thalamus (receptacle) at its tip. Four floral whorls — calyx, corolla, androecium, and gynoecium — are arranged on the thalamus. Calyx (sepals) and corolla (petals) are accessory organs; androecium and gynoecium are reproductive. Flowers may be bisexual (both whorls) or unisexual (one whorl). Symmetry may be actinomorphic (radial, e.g., mustard), zygomorphic (bilateral, e.g., pea), or asymmetric (e.g., canna).

Based on ovary position, flowers are hypogynous (superior ovary, e.g., mustard), perigynous (half-inferior ovary, e.g., rose), or epigynous (inferior ovary, e.g., guava). Aestivation describes petal/sepal arrangement in the bud: valvate (touching but not overlapping), twisted (each overlapping the next), imbricate (overlapping in no set direction), or vexillary (as in pea). Androecium stamens may be free or united (monoadelphous, diadelphous, polyadelphous), and attached to petals (epipetalous) or perianth (epiphyllous). Gynoecium carpels may be free (apocarpous) or fused (syncarpous), with varied placentation types.

The fruit is a matured ovary developed after fertilisation. Its wall (pericarp) may be dry or fleshy; fleshy pericarps are differentiated into epicarp, mesocarp, and endocarp. Fruits without fertilisation are called parthenocarpic. The drupe (e.g., mango, coconut) develops from monocarpellary superior ovaries and is one-seeded; in mango the mesocarp is fleshy and edible, while in coconut it is fibrous.

Seeds develop from ovules after fertilisation and consist of a seed coat and an embryo. Dicotyledonous seeds have a testa and tegmen (seed coat layers), hilum (attachment scar), micropyle, and two cotyledons with a radicle and plumule. Seeds may be endospermic (e.g., castor) or non-endospermic (e.g., pea). Monocotyledonous seeds (e.g., maize) are generally endospermic; the single cotyledon is the shield-shaped scutellum, the endosperm is bulky, and the embryo has coleoptile and coleorhiza protecting the plumule and radicle respectively.

A flowering plant is described in a definite sequence: habit, vegetative characters (root, stem, leaf), then floral characters (inflorescence, flower parts). Floral formula uses standard symbols — Br (bracteate), K (calyx), C (corolla), P (perianth), A (androecium), G (gynoecium), superior or inferior ovary indicators, and symmetry symbols. Fusion within a whorl is shown by brackets; adhesion between whorls by a line above symbols. A floral diagram visually maps the number, arrangement, and relations of floral parts in concentric whorls.

Family Solanaceae (potato family) is widely distributed in tropics, subtropics, and temperate zones. Vegetative characters: mostly herbs/shrubs, alternate simple leaves with reticulate venation. Floral characters: bisexual, actinomorphic flowers; five united sepals (valvate); five united petals (valvate); five epipetalous stamens; bicarpellary syncarpous superior ovary with axile placentation. Fruits are berries or capsules with many endospermous seeds. Economic importance: food (tomato, potato, brinjal), spice (chilli), medicine (belladonna, ashwagandha), fumigatory (tobacco), ornamentals (petunia).

Chapter 5 provides a comprehensive account of the external morphology of angiosperms, covering all major organs — root, stem, leaf, inflorescence, flower, fruit, and seed. Each organ is described with its typical structure, primary functions, and adaptive modifications. The chapter emphasises the use of precise technical terminology and systematic description as the foundation for plant classification and identification.

From an examination perspective, this chapter is critically important as it forms the basis of numerous CBSE board questions. Students must thoroughly understand the differences between tap and fibrous roots, types of venation, phyllotaxy, inflorescence, floral symmetry, ovary position, aestivation, placentation, and seed structure in mono- and dicots. The family Solanaceae provides a model for semi-technical plant description using floral formulae and diagrams — a skill directly tested in board examinations.