Morphology of Flowering Plants — NEET Notes

The root — types & regions

The flowering plant body is divided into an underground root system and an aerial shoot system. The root develops from the embryonic radicle, grows downward into the soil, lacks nodes, and is positively geotropic. Its functions are four: absorption of water and minerals, anchorage, food storage, and synthesis of plant growth regulators. NCERT recognises three classes of root system based on origin.

Regions of the root

From tip to base, every root passes through four anatomically distinct regions, and NEET has tested the boundary between them — particularly the location of root hairs.

Modifications of root

Roots get modified to perform functions other than absorption and anchorage. NEET groups these into three families.

The stem & its modifications

The stem is the ascending axis of the plant bearing branches, leaves, flowers, and fruits. It develops from the plumule of the embryo and is distinguished from the root by the presence of nodes and internodes, terminal and axillary buds, multicellular hair, and positively phototropic growth. Its primary function is to spread the photosynthetic leaves and conduct water, minerals, and photosynthates between root and shoot.

When stems take on functions other than support and conduction, they are said to be modified. NEET examiners love this section because identifying a particular modification — phylloclade, rhizome, corm, runner — is a clean one-mark question. Read NCERT's classification by location: underground, sub-aerial, and aerial.

The leaf, venation & phyllotaxy

The leaf is a lateral, generally flattened outgrowth of the stem developed exogenously at a node, with an axillary bud in its axil. Leaves arise from shoot apical meristems in acropetal order and are the chief photosynthetic organs. A typical leaf has three parts.

Venation — reticulate vs parallel

The arrangement of veins and veinlets in the lamina is termed venation. When veinlets form a network it is reticulate (dicot pattern, e.g., china rose, mango). When the veins run parallel to each other it is parallel (monocot pattern, e.g., banana, grass, maize). This is one of the easiest morphological tests for separating dicots from monocots.

Phyllotaxy — arrangement on the stem

Phyllotaxy is the pattern of arrangement of leaves on a stem. NCERT recognises three types — anchor each to its plant:

• Alternate: a single leaf at each node, in an alternating spiral — china rose, mustard, sunflower.
• Opposite: a pair of leaves at each node, lying opposite each other — Calotropis, guava.
• Whorled: more than two leaves at a node forming a ring — Alstonia.

Modifications of leaf

Leaves get modified into specialised structures when the photosynthetic role is taken over by the stem or when the plant needs support, defence, or storage. Five modifications appear in NEET frequently.

The inflorescence

A flower is a modified shoot in which the shoot apical meristem changes to a floral meristem, internodes do not elongate, and the axis condenses. The apex produces floral appendages laterally at successive nodes instead of leaves. When a shoot tip transforms into a single flower, the flower is solitary. The arrangement of flowers on a floral axis is the inflorescence, and NCERT distinguishes two major types based on the fate of the main axis.

The flower — symmetry & position

The flower is the angiosperm's reproductive unit. A typical flower bears four whorls successively on the swollen end of a stalk (the thalamus or receptacle): calyx, corolla, androecium, gynoecium. The first two are accessory, the latter two are reproductive. When calyx and corolla are indistinguishable, they are collectively termed perianth (as in lily). A flower bearing both stamens and carpels is bisexual; flowers with only one are unisexual.

Symmetry of the flower

• Actinomorphic (radial symmetry) — the flower can be divided into two equal halves by any vertical plane through its centre. Mustard, datura, chilli.
• Zygomorphic (bilateral symmetry) — only one vertical plane produces two similar halves. Pea, gulmohur, bean, Cassia.
• Asymmetric — no plane gives two similar halves. Canna.

Floral parts in multiples of 3, 4, or 5 are trimerous, tetramerous, or pentamerous. A flower borne in the axil of a small leaf-like bract is bracteate; without a bract, ebracteate.

Position of the ovary — hypogynous, perigynous, epigynous

Based on the relative position of calyx, corolla, and androecium with respect to the ovary on the thalamus, NCERT recognises three insertion types — and NEET tests this every alternate year.

Four floral whorls — the standard sequence

Every typical flower presents four concentric whorls in a fixed order from outside in. Learn them with their members, and the floral formula writes itself.

The basal end of a stamen's filament attaches to the thalamus or petal — NEET 2016 tested this directly. When stamens fuse with petals they are epipetalous (brinjal); fused with perianth, epiphyllous (lily). Free stamens are polyandrous. United into one bundle: monoadelphous (china rose). Two bundles: diadelphous (pea). More than two: polyadelphous (citrus). A sterile stamen is a staminode.

Aestivation — petal arrangement in the bud

Aestivation is the mode of arrangement of sepals or petals in the floral bud with respect to the other members of the same whorl. NCERT lists four types in corolla aestivation. NEET tests this with one-mark recall and as part of family identification.

Placentation — ovule arrangement in the ovary

After the stamens come the carpels. Inside each ovary, ovules attach to a cushion-like placenta. The arrangement of ovules and the geometry of the placenta is called placentation. NCERT recognises five types — and these are the most frequently asked one-marks in the chapter.

The easiest way to lock these in is to anchor each placentation to a single hallmark plant. Then any question becomes a process of elimination.

The fruit

A fruit is a characteristic feature of flowering plants — the mature, ripened ovary developed after fertilisation. A fruit formed without fertilisation is called parthenocarpic (e.g., banana). A typical fruit has a pericarp (wall) and seeds. The pericarp may be dry or fleshy; when fleshy, it differentiates into an outer epicarp, a middle mesocarp, and an inner endocarp.

NCERT distinguishes true fruits (developed only from the ovary) from false fruits (where the thalamus or other floral parts also contribute, as in apple). On structural basis, fruits are simple (one ovary), aggregate (many free carpels of one flower, e.g., lotus), or composite (entire inflorescence develops into a fruit, e.g., pineapple, jackfruit).

The NCERT chapter highlights two simple fleshy fruits — both drupes, both monocarpellary superior ovaries, both one-seeded:

• Mango drupe: epicarp thin, mesocarp fleshy and edible, endocarp stony and hard.
• Coconut drupe: epicarp thin, mesocarp fibrous (the coir), endocarp hard. NEET 2017 tested this as a direct one-mark.

The seed — dicot vs monocot

Ovules after fertilisation become seeds. Every seed has two essentials: a seed coat and an embryo. The embryo consists of an embryonal axis with a radicle at one end, a plumule at the other, and one or two cotyledons attached.

Three NCERT families — at a glance

NCERT presents three families in semi-technical descriptions; NEET asks one question from this section nearly every year (2016, 2021, 2022). For each family, three numbers and a placentation are usually enough — but you must also memorise the floral-formula symbols.

Solanaceae — the potato family

Mostly herbs and shrubs of the tropics and subtropics. Leaves alternate, simple, exstipulate, reticulate. Inflorescence solitary, axillary or cymose (as in Solanum). Flowers bisexual, actinomorphic, bracteate. Calyx 5, united, persistent, valvate. Corolla 5, united, valvate. Androecium 5 stamens, epipetalous. Gynoecium bicarpellary, syncarpous, obliquely placed; ovary superior, bilocular, axile placentation with many ovules. Fruit a berry or capsule; seeds many, endospermous. Members: tomato, brinjal, potato, chilli, tobacco, belladonna, petunia.

Fabaceae — the pea family

The Fabaceae (sub-family Papilionoideae of Leguminosae) is distributed worldwide. Leaves alternate, pinnately compound or simple, leaf base pulvinate, stipulate, reticulate. Inflorescence racemose. Flowers bisexual, zygomorphic, bracteate. Calyx 5, united (gamosepalous). Corolla 5 petals, vexillary aestivation — one standard, two wings, two keel petals. Androecium 10 stamens, diadelphous (9 + 1), dithecous anthers. Gynoecium monocarpellary; ovary superior, unilocular, marginal placentation, with many ovules. Fruit a legume; seeds non-endospermous. Members: pea, gram, beans, soybean, groundnut, Sesbania, indigofera. Economically the source of pulses (proteins), oil (soybean, groundnut), dye (indigofera), fibre (sunn hemp), ornament (lupin), and medicine (Cassia).

Liliaceae — the lily family

Distributed worldwide as ornamentals and vegetables. Mostly perennial herbs with underground bulbs/corms/rhizomes. Leaves mostly basal, alternate, with parallel venation. Inflorescence solitary or cymose. Flowers bisexual, actinomorphic, bracteate; perianth (calyx and corolla undifferentiated) of 6 tepals in two whorls of three, often united into a tube, with valvate aestivation. Androecium 6 stamens, epiphyllous. Gynoecium tricarpellary, syncarpous; ovary superior, trilocular, with axile placentation. Fruit a capsule, rarely a berry; seeds endospermous. Members: tulip, onion (Allium cepa), garlic, Aloe, Colchicum.