Morphology of Flowering Plants: NEET notes

1. Root systems and the root tip

NCERT §5.1, §5.1.1, Figures 5.1–5.3

• A flowering plant has two parts: the root system below the ground and the shoot system (stem, leaves, flowers, fruits) above it.
• Tap root system: in most dicots the radicle grows straight on into a primary root, which carries lateral roots of several orders called secondary, tertiary and so on. Example: mustard.
• Fibrous root system: in monocots the primary root lives only a short time; a large number of roots from the base of the stem take its place. Example: wheat.
• Adventitious roots grow from any part of the plant other than the radicle, as in grass, Monstera and the banyan tree.
• Roots absorb water and minerals, anchor the plant, store reserve food and synthesise plant growth regulators.
• Root cap: a thimble-shaped cover over the apex that shields the delicate tip as it pushes through the soil.
• Meristematic region: a few millimetres behind the cap. Its cells are very small and thin-walled, have dense protoplasm and keep dividing.
• Region of elongation: just behind the meristem. Its cells lengthen and enlarge rapidly, and this is what makes the root grow longer.
• Region of maturation: further back again, where cells differentiate. Some epidermal cells here grow into fine, thread-like root hairs, which take up water and minerals.

2. The stem

NCERT §5.2

• The stem is the part of the plant axis that grows upward. It carries branches, leaves, flowers and fruits, and it grows from the plumule of the embryo when the seed germinates.
• Nodes are the points where leaves arise; internodes are the lengths of stem between two neighbouring nodes.
• The stem carries buds, which are either terminal (at the tip) or axillary (in the angle between a leaf and the stem).
• A young stem is usually green; later it often becomes woody and dark brown.
• Its main work is to spread out the branches that hold leaves, flowers and fruits, and to conduct water, minerals and photosynthates.
• Some stems also store food, give support or protection, or reproduce the plant vegetatively.
• How to tell a stem from a root: nodes and internodes, multicellular hairs, and growth towards light (the stem is positively phototropic).

3. Leaf parts and venation

NCERT §5.3, §5.3.1, Figure 5.4

• A leaf is a flattened outgrowth on the side of the stem. It forms at a node and has a bud in its axil, and that axillary bud later grows into a branch.
• Leaves come from the shoot apical meristem and appear in acropetal order. They are the chief vegetative organs of photosynthesis.
• A typical leaf has three parts: leaf base, petiole and lamina. The leaf base joins the leaf to the stem and may carry two small leaf-like stipules.
• In monocots the leaf base broadens into a sheath that wraps the stem partly or fully. In some legumes the leaf base is swollen; this is the pulvinus.
• The petiole holds the blade up to the light. A long, thin, flexible petiole lets the blade flutter in the wind, which cools the leaf and brings fresh air to its surface.
• The lamina is the green, expanded blade with veins and veinlets; the prominent middle vein is the midrib. Veins keep the blade rigid and carry water, minerals and food.
• Leaves differ in the shape, margin, apex, surface and depth of incision of the lamina.
• Venation is how veins and veinlets are laid out in the lamina. Reticulate: veinlets form a network, usual in dicots. Parallel: veins run side by side, typical of most monocots.

4. Compound leaves and phyllotaxy

NCERT §5.3.2, §5.3.3, Figures 5.5–5.6

• Simple leaf: the lamina is entire, or its incisions stop short of the midrib.
• Compound leaf: the incisions go all the way to the midrib and split the lamina into separate leaflets.
• A bud sits in the axil of the petiole of both simple and compound leaves, but never in the axil of a leaflet. This is how a leaflet is told apart from a whole leaf.
• Pinnately compound: many leaflets on one common axis, the rachis, which stands for the midrib. Example: neem.
• Palmately compound: all the leaflets are attached at one point, the tip of the petiole. Example: silk cotton.
• Phyllotaxy is the pattern in which leaves are arranged on a stem or branch. There are three usual types.
• Alternate: one leaf at each node, placed alternately, as in china rose, mustard and sunflower.
• Opposite: two leaves at each node, facing each other, as in Calotropis and guava.
• Whorled: more than two leaves at a node, forming a ring, as in Alstonia.

5. Racemose and cymose inflorescence

NCERT §5.4, Figures 5.7–5.8

• A flower is a modified shoot. The shoot apical meristem turns into a floral meristem, the internodes stay short so the axis is condensed, and the apex produces floral appendages at successive nodes in place of leaves.
• When a shoot tip itself becomes a flower, that flower is always solitary.
• Inflorescence: the way flowers are arranged on the floral axis.
• The two major types are defined by one question: does the apex turn into a flower, or does it keep growing?
• Racemose: the main axis goes on growing, and flowers are borne on its sides in acropetal succession, so the oldest flowers are at the base and the youngest near the tip.
• Cymose: the main axis ends in a flower, so its growth is limited, and the flowers open in basipetal order, the oldest at the top.

6. Flower whorls and symmetry

NCERT §5.5, §5.5.1, Figure 5.10

• The flower is the reproductive unit of angiosperms and serves sexual reproduction.
• A typical flower has four whorls, one above another, on the swollen tip of the pedicel called the thalamus or receptacle: calyx, corolla, androecium and gynoecium.
• Calyx and corolla are accessory organs; androecium and gynoecium are the reproductive organs.
• When calyx and corolla cannot be told apart, as in lily, together they are called the perianth.
• Bisexual flower: has both androecium and gynoecium. Unisexual flower: has only stamens or only carpels.
• Actinomorphic (radial symmetry): any radial plane through the centre cuts it into two equal halves. Examples: mustard, datura, chilli.
• Zygomorphic (bilateral symmetry): only one particular vertical plane gives two similar halves. Examples: pea, gulmohur, bean, Cassia.
• Asymmetric (irregular): no vertical plane through the centre gives two similar halves. Example: canna.
• Trimerous, tetramerous and pentamerous flowers have floral appendages in multiples of 3, 4 and 5.
• A bract is a reduced leaf at the base of the pedicel. Flowers with bracts are bracteate; flowers without them are ebracteate.

7. Ovary position on the thalamus

NCERT §5.5, Figure 5.9

• Flowers are classed by where the calyx, corolla and androecium sit on the thalamus compared with the ovary: hypogynous, perigynous or epigynous.
• Hypogynous: the gynoecium is at the top and every other part is attached below it. The ovary is superior. Examples: mustard, china rose, brinjal.
• Perigynous: the gynoecium is in the centre and the other parts sit on the rim of the thalamus at nearly the same level. The ovary is half inferior. Examples: plum, rose, peach.
• Epigynous: the margin of the thalamus grows up around the ovary, encloses it fully and fuses with it, so the other parts arise above the ovary. The ovary is inferior. Examples: guava, cucumber and the ray florets of sunflower.
• Superior, half inferior and inferior describe the ovary; hypogynous, perigynous and epigynous describe the flower. The terms come in matched pairs.
• Quick check: if you see the sepals and petals attached on top of the ovary, as at the crown of a guava fruit, the ovary was inferior.

8. Calyx, corolla and aestivation

NCERT §5.5.1.1, §5.5.1.2, Figure 5.11

• Calyx: the outermost whorl, made of sepals. Sepals are usually green and leaf-like and protect the flower while it is a bud.
• Gamosepalous: sepals united. Polysepalous: sepals free.
• Corolla: made of petals, whose bright colours usually serve to draw insects in for pollination. Gamopetalous: petals united. Polypetalous: petals free.
• Corolla form varies a great deal. Common shapes: a tube (tubular), a bell, a funnel, or a flat wheel.
• Aestivation is the way sepals or petals lie in the bud relative to their neighbours in the same whorl. Main types: valvate, twisted, imbricate, vexillary.
• Valvate: neighbouring members just meet at their edges and do not overlap. Example: Calotropis.
• Twisted: each member overlaps the next one with one margin, all the way round in one direction. Examples: china rose, lady's finger, cotton.
• Imbricate: the margins overlap, but with no single direction. Examples: Cassia, gulmohur.
• Vexillary or papilionaceous (pea, bean): five petals; the largest, the standard, overlaps the two lateral wings, and the wings overlap the two smallest anterior petals, the keel.

9. Androecium

NCERT §5.5.1.3

• The androecium is made of stamens. Each stamen is a male reproductive organ with a stalk, the filament, and an anther.
• An anther normally has two lobes, and every lobe holds two pollen-sacs, the chambers in which pollen grains form. A typical anther therefore has four pollen-sacs.
• A sterile stamen is called a staminode.
• Epipetalous: stamens attached to the petals, as in brinjal. Epiphyllous: stamens attached to the perianth, as in lily.
• Polyandrous: the stamens stay free of each other.
• Monoadelphous: stamens united into one bundle, as in china rose. Diadelphous: two bundles, as in pea. Polyadelphous: more than two bundles, as in citrus.
• Filament length can differ among the stamens of one flower, as in Salvia and mustard.

10. Gynoecium and placentation

NCERT §5.5.1.4, Figure 5.12

• The gynoecium is the flower's female reproductive part, made of one or more carpels.
• A carpel has three parts: the ovary (the enlarged base), the style (a long tube above it) and the stigma (usually at the tip of the style), which is the surface that receives pollen.
• Each ovary carries one or more ovules attached to a flat, cushion-like placenta.
• Apocarpous: two or more carpels that stay free, as in lotus and rose. Syncarpous: carpels fused, as in mustard and tomato.
• After fertilisation the ovules become seeds and the ovary ripens into a fruit.
• Placentation is the arrangement of ovules inside the ovary.
• Marginal: the placenta is a ridge along the ventral suture and the ovules sit on it in two rows. Example: pea.
• Axile: a multilocular ovary with the placenta along its central axis, carrying the ovules. Examples: china rose, tomato, lemon.
• Parietal: ovules grow on the inner wall of the ovary. The ovary is one-chambered but becomes two-chambered by a false septum. Examples: mustard, Argemone.
• Free central: ovules on a central axis with no septa (Dianthus, Primrose). Basal: the placenta is at the base of the ovary and bears a single ovule (sunflower, marigold).

11. Fruit and seed

NCERT §5.6, §5.7, Figures 5.13–5.15

• The fruit is a feature found only in flowering plants. It is the mature, ripened ovary formed after fertilisation. A fruit formed without fertilisation is parthenocarpic.
• A fruit has a wall, the pericarp, around its seeds. The pericarp can be dry or fleshy; a thick fleshy one is divided into outer epicarp, middle mesocarp and inner endocarp.
• Drupe: a one-seeded fruit from a monocarpellary superior ovary, as in mango and coconut. Mango: thin epicarp, fleshy edible mesocarp, stony hard endocarp. Coconut: fibrous mesocarp.
• Ovules become seeds after fertilisation. A seed is a seed coat around an embryo; the embryo has a radicle, an embryonal axis and one cotyledon (wheat, maize) or two (gram, pea).
• Dicot seed coat: outer testa and inner tegmen. The hilum is the scar where the seed was attached to the fruit; the micropyle is a small pore just above the hilum.
• Dicot embryo: an embryonal axis with the radicle at one end and the plumule at the other, plus two cotyledons, which are frequently fleshy stores of reserve food.
• Endospermic seeds keep a food-storing endosperm formed by double fertilisation, as in castor. In bean, gram and pea the mature seed has no endosperm (non-endospermous).
• Monocot seeds are generally endospermic; orchid seeds are an exception. In maize the membranous seed coat is fused with the fruit wall, and the bulky endosperm stores food.
• The maize endosperm is covered by a proteinous aleurone layer. The small embryo lies in a groove at one end; it has one large shield-shaped cotyledon, the scutellum, and a short axis whose plumule is sheathed by the coleoptile and whose radicle is sheathed by the coleorhiza.

12. Floral formula and Solanaceae

NCERT §5.8, §5.9, Figures 5.16–5.17

• A semi-technical description is short, simple and scientific, and follows a fixed order: habit, then vegetative characters (root, stem, leaves), then floral characters (inflorescence, flower parts), then a floral diagram and a floral formula.
• Floral formula symbols: Br bracteate, K calyx, C corolla, P perianth, A androecium, G gynoecium, ⊕ actinomorphic, % zygomorphic, ⚥ bisexual, ♂ male, ♀ female. A line under G means a superior ovary; a line over G means an inferior ovary.
• Fusion within a whorl is shown by putting the number in brackets, e.g. C(5). Adhesion between whorls is shown by a line drawn over the symbols concerned, e.g. over C and A for epipetalous stamens.
• A floral diagram shows the number of parts, their arrangement and their relation to one another. A dot at the top marks the mother axis; calyx is the outermost ring and gynoecium the centre.
• The worked example (Figure 5.16) is mustard, family Brassicaceae: ⊕ ⚥ K2+2 C4 A2+4 G(2), ovary superior.
• Solanaceae, the potato family, is a large family spread through the tropics, subtropics and temperate zones. Example figured: Solanum nigrum (makoi).
• Vegetative: mostly herbs and shrubs, rarely small trees. Stem herbaceous (rarely woody); potato (Solanum tuberosum) has an underground stem. Leaves alternate and simple (rarely pinnately compound), without stipules (exstipulate), with reticulate venation.
• Floral: inflorescence solitary, axillary or cymose; flower bisexual and actinomorphic; five united, persistent sepals and five united petals, both valvate; five epipetalous stamens; bicarpellary, obliquely placed, syncarpous, superior, bilocular ovary with a swollen placenta bearing many ovules (axile). Fruit berry or capsule; seeds many, endospermous.
• Floral formula: ⊕ ⚥ K(5) C(5) A5 G(2), with a line joining C and A (epipetalous) and the ovary superior.
• Uses: tomato, brinjal and potato are foods; chilli is a spice; belladonna and ashwagandha are medicines; tobacco is fumigatory; petunia is an ornamental.

Must-know facts

1. Tap root: mustard. Fibrous root: wheat. Adventitious roots: grass, Monstera, banyan.
2. Root tip from apex back: root cap, meristematic region, region of elongation, region of maturation (root hairs).
3. Stem grows from the plumule; root from the radicle. Only the stem has nodes and internodes.
4. Leaf base sheath: monocots. Pulvinus: swollen leaf base in some legumes.
5. Reticulate venation: dicots. Parallel venation: most monocots.
6. Axillary bud: in the axil of the petiole, never in the axil of a leaflet.
7. Pinnately compound: neem (rachis). Palmately compound: silk cotton.
8. Phyllotaxy: alternate (china rose, mustard, sunflower), opposite (Calotropis, guava), whorled (Alstonia).
9. Racemose: axis keeps growing, acropetal. Cymose: axis ends in a flower, basipetal.
10. Actinomorphic: mustard, datura, chilli. Zygomorphic: pea, gulmohur, bean, Cassia. Asymmetric: canna.
11. Superior ovary (hypogynous): mustard, china rose, brinjal. Half inferior (perigynous): plum, rose, peach. Inferior (epigynous): guava, cucumber, sunflower ray florets.
12. Aestivation: valvate (Calotropis), twisted (china rose, lady's finger, cotton), imbricate (Cassia, gulmohur), vexillary (pea, bean).
13. Epipetalous: brinjal. Epiphyllous: lily. Monoadelphous: china rose. Diadelphous: pea. Polyadelphous: citrus.
14. Apocarpous: lotus, rose. Syncarpous: mustard, tomato.
15. Placentation: marginal (pea), axile (china rose, tomato, lemon), parietal (mustard, Argemone), free central (Dianthus, Primrose), basal (sunflower, marigold).
16. Drupe: mango and coconut, from a monocarpellary superior ovary, one-seeded; coconut mesocarp is fibrous.
17. Endospermic dicot: castor. Non-endospermous: bean, gram, pea. Non-endospermic monocot: orchids.
18. Maize seed: aleurone layer, scutellum, coleoptile over the plumule, coleorhiza over the radicle.
19. Mustard (Brassicaceae): ⊕ ⚥ K2+2 C4 A2+4 G(2).
20. Solanaceae: ⊕ ⚥ K(5) C(5) A5 G(2), epipetalous, axile placentation, berry or capsule.

Common traps

Key terms

Adventitious root

A root that grows from any part other than the radicle.

Root cap

The thimble-shaped cover protecting the root apex.

Node

The point on a stem where leaves arise; the stretch between two nodes is an internode.

Pulvinus

The swollen leaf base seen in some leguminous plants.

Rachis

The common axis of a pinnately compound leaf, standing for its midrib.

Phyllotaxy

The pattern in which leaves are arranged on a stem or branch.

Inflorescence

The way flowers are arranged on the floral axis.

Thalamus

The swollen end of the pedicel on which the floral whorls sit; also called the receptacle.

Perianth

Calyx and corolla together when they cannot be told apart, as in lily.

Aestivation

How sepals or petals are arranged in the bud relative to others of the same whorl.

Staminode

A sterile stamen.

Epipetalous

Stamens attached to the petals.

Syncarpous

A gynoecium whose carpels are fused; free carpels are apocarpous.

Placentation

The arrangement of ovules inside the ovary.

Parthenocarpic fruit

A fruit formed without fertilisation of the ovary.

Drupe

A one-seeded fruit from a monocarpellary superior ovary with a stony endocarp, such as mango.

Hilum

The scar on the seed coat where the seed was attached to the fruit.

Scutellum

The single large shield-shaped cotyledon of a cereal embryo.

Aleurone layer

The proteinous outer layer of the endosperm in a maize grain.

Coleoptile

The sheath around the plumule of a monocot embryo; the coleorhiza sheaths the radicle.