Morphology of Flowering Plants

2.1 Core concepts

• Angiosperms, despite vast diversity, are universally characterised by roots, stems, leaves, flowers and fruits; the underground part is the root system, the part above ground is the shoot system (NCERT §5, p. 57; §5.1 intro, p. 57–58).
• In most dicots the radicle elongates directly into a primary root, which bears secondary and tertiary lateral roots — together the tap root system (e.g. mustard) (NCERT §5.1, p. 57–58).
• In monocots the primary root is short-lived and is replaced by many roots arising from the base of the stem, forming the fibrous root system (e.g. wheat) (NCERT §5.1, p. 58).
• Adventitious roots arise from parts of the plant other than the radicle, e.g. grass, Monstera, banyan (NCERT §5.1, p. 58).
• Root functions: absorption of water and minerals, anchorage, storage of reserve food, and synthesis of plant growth regulators (NCERT §5.1, p. 58).
• The root tip shows four distinct regions in acropetal order: root cap (thimble-like, protective) → region of meristematic activity (small, thin-walled, dense protoplasm, dividing cells) → region of elongation (cells enlarge and elongate, drive root growth in length) → region of maturation (cells differentiate; some epidermal cells produce root hairs that absorb water and minerals) (NCERT §5.1.1, p. 59).
• The stem is the ascending axis bearing branches, leaves, flowers and fruits; it develops from the plumule of the embryo, bears nodes (where leaves arise) and internodes (region between nodes), and bears terminal or axillary buds (NCERT §5.2, p. 59).
• Stem functions: spreading branches, conducting water/minerals/photosynthates, and in some plants storage of food, support, protection and vegetative propagation (NCERT §5.2, p. 59).
• The leaf is a lateral, generally flattened structure borne at the node with a bud in its axil; leaves originate from the shoot apical meristem in acropetal order and are the most important vegetative organs for photosynthesis (NCERT §5.3, p. 59).
• A typical leaf has three parts — leaf base, petiole, lamina; the leaf base may bear two lateral stipules, expand into a sheath in monocots, or become swollen as the pulvinus in some legumes (NCERT §5.3, p. 60).
• Venation is the arrangement of veins/veinlets in the lamina: reticulate (network — typical of dicots) and parallel (typical of monocots) (NCERT §5.3.1, p. 60).
• Leaves are simple when the lamina is entire or incised but incisions do not reach the midrib; compound when incisions reach the midrib breaking it into leaflets. A bud is present in the axil of the petiole but never in the axil of leaflets (NCERT §5.3.2, p. 60).
• Compound leaves are pinnately compound (leaflets on a common axis, the rachis — e.g. neem) or palmately compound (leaflets attached at a common point at the tip of the petiole — e.g. silk cotton) (NCERT §5.3.2, p. 60–61).
• Phyllotaxy — arrangement of leaves on stem/branch: alternate (single leaf per node — china rose, mustard, sunflower), opposite (pair per node — Calotropis, guava), whorled (more than two per node — Alstonia) (NCERT §5.3.3, p. 61).
• Inflorescence is the arrangement of flowers on the floral axis; the shoot apical meristem becomes a floral meristem, internodes do not elongate, and the axis condenses. A solitary flower results when the shoot tip itself becomes a flower (NCERT §5.4, p. 61).
• Two major types: racemose — main axis continues to grow, flowers borne laterally in acropetal succession; cymose — main axis terminates in a flower, growth limited, flowers borne in basipetal order (NCERT §5.4, p. 61–62).
• The flower is the reproductive unit of angiosperms with four whorls on the thalamus/receptacle: calyx, corolla (accessory), androecium and gynoecium (reproductive). In lily the calyx and corolla are indistinct and together called the perianth. Bisexual flowers have both stamens and carpels; unisexual have only one (NCERT §5.5, p. 62).
• Symmetry: actinomorphic (radial — mustard, datura, chilli), zygomorphic (bilateral — pea, gulmohur, bean, Cassia), asymmetric (canna). Flowers are trimerous/tetramerous/pentamerous if parts come in multiples of 3/4/5; bracteate if bracts are present at the base of the pedicel, otherwise ebracteate (NCERT §5.5, p. 62).
• Position of ovary on thalamus: hypogynous — ovary superior, other parts below (mustard, china rose, brinjal); perigynous — ovary half-inferior, other parts on the thalamus rim at the same level (plum, rose, peach); epigynous — ovary inferior, thalamus encloses and fuses with ovary, other parts arise above (guava, cucumber, ray florets of sunflower) (NCERT §5.5, p. 63).
• Calyx = sepals (outermost, green, protective); gamosepalous (united) or polysepalous (free). Corolla = petals (often coloured, attract pollinators); gamopetalous or polypetalous; shapes — tubular, bell-, funnel-, wheel-shaped (NCERT §5.5.1.1–5.5.1.2, p. 63).
• Aestivation — arrangement of sepals/petals in the bud: valvate (margins touch, no overlap — Calotropis), twisted (one margin overlaps the next consistently — china rose, lady's finger, cotton), imbricate (overlap not in any particular direction — Cassia, gulmohur), vexillary/papilionaceous (standard overlaps two wings which overlap two keel petals — pea, bean) (NCERT §5.5.1.2, p. 63–64).
• Androecium = stamens; each stamen has a filament and an anther; anther is usually bilobed with two pollen-sacs per lobe. A sterile stamen is a staminode. Stamens may be epipetalous (attached to petals — brinjal), epiphyllous (attached to perianth — lily), polyandrous (free), monoadelphous (one bundle — china rose), diadelphous (two bundles — pea), polyadelphous (more than two bundles — citrus); filament length may vary within a flower (Salvia, mustard) (NCERT §5.5.1.3, p. 64).
• Gynoecium = female part of one or more carpels; carpel has stigma, style and ovary; ovules sit on the cushion-like placenta. Multiple carpels are apocarpous if free (lotus, rose) or syncarpous if fused (mustard, tomato). After fertilisation, ovules become seeds and the ovary matures into a fruit (NCERT §5.5.1.4, p. 65).
• Placentation — arrangement of ovules within the ovary: marginal (ovules on a ridge along the ventral suture — pea); axile (placenta is axial in a multilocular ovary — china rose, tomato, lemon); parietal (ovules on inner wall; one-chambered ovary becomes two-chambered by a false septum — mustard, Argemone); free central (ovules on central axis with no septa — Dianthus, primrose); basal (single ovule at the base — sunflower, marigold) (NCERT §5.5.1.4, p. 65).
• The fruit is a mature/ripened ovary developed after fertilisation; a fruit formed without fertilisation is parthenocarpic. Fruit wall = pericarp (dry or fleshy); if fleshy, differentiates into epicarp / mesocarp / endocarp (NCERT §5.6, p. 65).
• A drupe develops from a monocarpellary superior ovary and is one-seeded: mango (thin epicarp, fleshy edible mesocarp, stony endocarp) and coconut (fibrous mesocarp) (NCERT §5.6, p. 65–66).
• The seed = seed coat + embryo (radicle + embryonal axis + one cotyledon as in wheat/maize OR two cotyledons as in gram/pea) (NCERT §5.7, p. 66).
• Dicot seed: seed coat has outer testa and inner tegmen; hilum is the scar where the seed was attached to the fruit; micropyle is a small pore above the hilum; embryo has two cotyledons (often fleshy with reserve food) plus radicle and plumule. Seeds with persistent endosperm (from double fertilisation) are endospermic (castor); without endosperm in mature stage are non-endospermous (bean, gram, pea) (NCERT §5.7.1, p. 66).
• Monocot seed: generally endospermic (orchids are exceptions). In cereals like maize the seed coat is membranous and fused with the fruit wall; the bulky endosperm stores food and is separated from the embryo by a proteinous aleurone layer. The embryo has one large shield-shaped cotyledon called the scutellum and a short axis; the plumule is enclosed by the coleoptile and the radicle by the coleorhiza (NCERT §5.7.2, p. 66–67).
• Semi-technical description proceeds in order: habit → vegetative characters (root, stem, leaves) → floral characters (inflorescence, flower parts) → floral diagram and floral formula (NCERT §5.8, p. 67).
• Floral formula symbols: Br = bracteate, K = calyx, C = corolla, P = perianth, A = androecium, G = gynoecium; G with a line below = superior ovary, G with a line above = inferior ovary; ♂ = male, ♀ = female, ⚥ = bisexual; ⊕ = actinomorphic, %/↑ = zygomorphic; fusion shown by enclosing the figure in brackets, adhesion by a line above the symbols (NCERT §5.8, p. 67–68).
• A floral diagram shows the number, arrangement and relations of floral parts; the position of the mother axis is indicated by a dot at the top, and whorls are drawn from calyx (outermost) to gynoecium (centre) (NCERT §5.8, p. 68). The mustard floral formula illustrated is ⊕ ⚥ K₂₊₂ C₄ A₂₊₄ G₍₂₎ (Family: Brassicaceae) (NCERT Figure 5.16, p. 67–68).
• Solanaceae (potato family) — widely distributed in tropical, subtropical and temperate zones; mostly herbs/shrubs, rarely small trees. Leaves alternate, simple (rarely pinnately compound), exstipulate, reticulate venation. Underground stem in potato (Solanum tuberosum) (NCERT §5.9, p. 68).
• Solanaceae floral characters: inflorescence solitary/axillary or cymose; flowers bisexual, actinomorphic; calyx 5, united, persistent, valvate; corolla 5, united, valvate; androecium 5, epipetalous; gynoecium bicarpellary syncarpous, ovary superior, bilocular, axile placentation with swollen placenta and many ovules; fruit berry or capsule; seeds many, endospermous. Floral formula: ⊕ ⚥ K₍₅₎ C₍₅₎ A₅ G₍₂₎ (NCERT §5.9, p. 69).
• Solanaceae economic importance: food (tomato, brinjal, potato), spice (chilli), medicine (belladonna, ashwagandha), fumigatory (tobacco), ornamentals (petunia) (NCERT §5.9, p. 69).

2.2 Definitions to memorise

2.3 Diagrams / processes to remember

• Figure 5.1 — Parts of a flowering plant (mustard) showing shoot system (stem, leaf, bud, flower, fruit, node, internode) and root system (primary, secondary) — p. 58.
• Figure 5.2 — Tap, fibrous, adventitious roots with main root + laterals (tap), tuft of fibrous roots, and stem-borne adventitious roots — p. 58.
• Figure 5.3 — Regions of the root tip: root cap, region of meristematic activity, region of elongation, region of maturation (with root hairs) — p. 59.
• Figure 5.4 — Leaf parts and venation: lamina, petiole, stipule, leaf base, axillary bud; reticulate vs. parallel venation — p. 60.
• Figure 5.5 — Compound leaves: pinnately compound (neem, with rachis) and palmately compound (silk cotton) — p. 60.
• Figure 5.6 — Phyllotaxy: alternate (china rose), opposite (guava), whorled (Alstonia) — p. 61.
• Figures 5.7 and 5.8 — Racemose vs. cymose inflorescence — p. 61–62.
• Figure 5.9 — Position of floral parts on the thalamus: hypogynous, perigynous (two views), epigynous — p. 62.
• Figure 5.10 — Parts of a flower: pedicel, calyx, corolla, androecium, gynoecium — p. 63.
• Figure 5.11 — Aestivation in corolla: valvate, twisted, imbricate, vexillary — p. 64.
• Figure 5.12 — Placentation types: marginal, axile, parietal, free central, basal — p. 65.
• Figure 5.13 — Parts of a fruit: mango and coconut, showing epicarp, mesocarp, endocarp — p. 66.
• Figure 5.14 — Dicot seed structure: seed coat, hilum, micropyle, cotyledon, plumule, radicle — p. 66.
• Figure 5.15 — Monocot (maize) seed structure: seed coat + fruit wall, aleurone layer, endosperm, scutellum, coleoptile, plumule, radicle, coleorhiza — p. 67.
• Figure 5.16 — Floral diagram with floral formula (mustard, Brassicaceae) — p. 67.
• **Figure 5.17 — Solanaceae case (Solanum nigrum, makoi)**: flowering twig, flower, L.S. of flower, stamens, carpel, floral diagram — p. 68.

2.4 Common confusions / NTA trap points

• Acropetal vs. basipetal: racemose = acropetal (older flowers below, younger above); cymose = basipetal (older above, younger below). "Acropetal" describes racemose inflorescence and "basipetal" describes cymose (NCERT §5.4, p. 61–62).
• Hypogynous vs. perigynous vs. epigynous is about the position of the ovary relative to other floral parts on the thalamus, not the position of the stamens. Examples to memorise verbatim: mustard/china rose/brinjal (hypogynous), plum/rose/peach (perigynous), guava/cucumber/ray florets of sunflower (epigynous) (NCERT §5.5, p. 63).
• Parietal vs. axile: in parietal placentation the ovary becomes two-chambered only because of a false septum (mustard, Argemone); axile has true septa with a multilocular ovary (china rose, tomato, lemon) (NCERT §5.5.1.4, p. 65).
• Vexillary aestivation is a specific overlap pattern of five petals (standard > wings > keel) — confined to pea/bean family — not just "any overlapping petals" (NCERT §5.5.1.2, p. 64).
• Drupe is defined by ovary type (monocarpellary, superior, one-seeded), not by being fleshy. Coconut is a drupe despite having a fibrous mesocarp (NCERT §5.6, p. 65–66).
• Scutellum is a cotyledon, not the endosperm. The aleurone layer is proteinous and lies between the endosperm and the embryo in maize-type seeds (NCERT §5.7.2, p. 67).
• A bud is in the axil of the petiole of a compound leaf — never in the axil of individual leaflets. This is a frequent distractor (NCERT §5.3.2, p. 60).