Morphology of Flowering Plants

The flowering-plant body is divided into an underground root system and an aerial shoot system. The root is the descending, usually non-green part that anchors the plant, absorbs water and minerals, stores food and conducts these to the stem. There are three systems: the tap root of dicots (a primary root with branches, e.g. mustard), the fibrous root of monocots (a cluster of thin roots from the stem base, e.g. wheat) and adventitious roots arising from parts other than the radicle (e.g. Monstera, grass). The tip of a young root shows four zones in sequence — the protective root cap, then the regions of meristematic activity, elongation, and maturation (which bears the root hairs).

Roots are often modified for special functions, and matching modification to example is a guaranteed NEET mark. Tap roots store food and become swollen as conical (carrot), fusiform (radish) or napiform (turnip). Adventitious roots also store food (the tuberous root of sweet potato). For mechanical support, banyan develops hanging prop roots and maize/sugarcane develop stilt roots. In swampy mangroves like Rhizophora, roots grow vertically upward as pneumatophores to obtain oxygen.

The stem is the ascending axis that develops from the plumule and bears nodes (where leaves arise) and internodes; it carries buds, leaves, flowers and fruits, conducts materials, and may store food or help in support and propagation. Young stems are usually green and photosynthetic. As with roots, NEET focuses heavily on stem modifications, which are grouped as underground, sub-aerial and aerial.

Underground stems store food and survive unfavourable seasons: the tuber of potato (with 'eyes' that are nodes), the rhizome of ginger, the bulb of onion and the corm of Colocasia. Sub-aerial modifications help vegetative spread — the runner (grass), stolon (mint), offset (water hyacinth) and sucker (chrysanthemum). Aerial modifications include stem tendrils for climbing (gourds, grapevine), thorns for protection (Citrus, Bougainvillea) and flattened green phylloclades that photosynthesise in xerophytes (Opuntia). The clue is that any structure arising in the axil of a leaf or bearing nodes is a modified stem, not a root.

The leaf is a flattened lateral outgrowth of the stem, borne at a node and bearing a bud in its axil; it is the chief organ of photosynthesis and transpiration. A typical leaf has three parts: the leaf base (which may bear stipules or, in monocots, sheathe the stem), the petiole (stalk) and the broad green lamina (blade) with its veins. NEET commonly tests the features that separate dicot and monocot leaves, beginning with venation.

Venation is the arrangement of veins in the lamina. In reticulate venation the veinlets form a network, typical of dicots (e.g. peepal); in parallel venation the veins run parallel, typical of monocots (e.g. grasses, banana). Leaves are also classified as simple (a single, possibly incised, lamina) or compound, where the lamina is divided into leaflets. Compound leaves are pinnately compound (leaflets on a common axis, the rachis — neem) or palmately compound (leaflets from a common point — silk cotton).

Phyllotaxy is the pattern in which leaves are arranged on the stem, and three patterns are examinable: alternate (one leaf per node, e.g. sunflower, mustard), opposite (two leaves per node, e.g. Calotropis, guava) and whorled (more than two leaves per node, e.g. Alstonia). This arrangement maximises light capture while minimising shading of lower leaves.

Like roots and stems, leaves are frequently modified to carry out functions other than photosynthesis. They become tendrils for climbing (pea), spines for defence and reduced water loss (cacti), fleshy storage leaves (onion, garlic), and a phyllode — a flattened green petiole that replaces the leaf in Australian Acacia. In insectivorous plants the whole leaf is modified into a pitcher (Nepenthes) or a trap (Venus flytrap) to capture insects for nitrogen. Recognising whether a tendril or spine is a modified leaf or stem (by its position) is a classic NEET discrimination.

An inflorescence is the arrangement of flowers on the floral axis. NCERT recognises two main types. In a racemose inflorescence the main axis continues to grow and bears flowers laterally in acropetal succession (the oldest flowers at the base and the youngest near the growing tip). In a cymose inflorescence the main axis terminates in a flower, so its growth is limited, and the flowers are borne in basipetal order. Reading off the succession (acropetal vs basipetal) is a quick NEET identifier.

The flower is the reproductive unit of angiosperms, built of four whorls on the swollen tip of the stalk, the thalamus. From outside in these are the calyx (sepals, usually green and protective), the corolla (petals, often coloured to attract pollinators), the androecium (stamens, the male whorl, each with anther and filament) and the gynoecium (carpels/pistil, the female whorl, each with stigma, style and ovary). A flower with all four whorls is complete; one with both androecium and gynoecium is bisexual.

Flowers are described by their symmetry and the position of the ovary. Actinomorphic flowers are radially symmetrical, divisible into equal halves by any vertical plane (mustard, Datura); zygomorphic flowers are bilaterally symmetrical, divisible into equal halves by only one plane (pea, Cassia). By the position of the ovary on the thalamus a flower is hypogynous (ovary superior, other parts below — mustard), perigynous (ovary half-inferior, parts at the rim — rose, plum) or epigynous (ovary inferior, parts above — guava, cucumber, ray florets of sunflower).

Two more terms describe the internal arrangement and are very high-yield. Aestivation is the mode of arrangement of sepals or petals in the floral bud: valvate (margins touching, not overlapping — Calotropis), twisted (one margin overlaps the next regularly — China rose), imbricate (overlapping but not in a set direction — Cassia) and vexillary (the pea pattern with a large standard, two wings and a keel). Placentation is the arrangement of ovules within the ovary: marginal (pea), axile (China rose, tomato, lemon), parietal (mustard, Argemone), free-central (Dianthus, primrose) and basal (sunflower, marigold). Memorising one classic example per type of aestivation and placentation reliably scores marks.

After fertilisation the ovary matures into a fruit and the ovules into seeds. A fruit has a wall, the pericarp, which may be dry or differentiated into three layers — epicarp, mesocarp and endocarp — as in the drupe of mango and coconut (fleshy mesocarp, stony endocarp). A fruit formed only from the ovary is a true fruit; when other floral parts such as the thalamus also contribute it is a false fruit (apple). A fruit that develops without fertilisation is parthenocarpic and seedless (banana).

The seed is the fertilised ovule, made of a seed coat and an embryo. A typical dicot seed (e.g. gram, pea) is usually non-endospermic: the food is stored in two thick cotyledons, and the seed coat shows a hilum (scar) and a tiny micropyle; the embryo has a radicle and plumule. A typical monocot seed (e.g. maize) is endospermic: the food is stored in the endosperm guarded by a proteinaceous aleurone layer, and the single cotyledon (the scutellum) has a sheath over the plumule (coleoptile) and over the radicle (coleorhiza).

NCERT then studies three plant families through their semi-technical (floral) features, and these are recurring NEET favourites. Fabaceae (Papilionoideae) have roots with nitrogen-fixing nodules, pinnately compound leaves, a zygomorphic bisexual flower with vexillary aestivation, ten stamens that are diadelphous (9 fused + 1 free), a superior ovary with marginal placentation, and the fruit a legume (pod). Examples include gram, pea, groundnut and Sesbania; the family also yields pulses, the dye indigo (Indigofera) and fibres (sunhemp).

Solanaceae have an actinomorphic, bisexual flower with five united sepals and petals, five epipetalous stamens, a bicarpellary syncarpous superior ovary with axile placentation, and the fruit a berry or capsule; examples are potato, tomato, brinjal, tobacco and Datura. Liliaceae, a monocot family, have an actinomorphic, trimerous flower with a perianth of six tepals (3+3), six stamens, a tricarpellary syncarpous superior ovary with axile placentation, and a capsule or berry; examples are tulip, Gloriosa, Allium (onion, garlic), aloe and asparagus. The cleanest revision is a single line per family: fruit type + aestivation/placentation + a flagship example.