Morphology of Flowering Plants – Comprehensive Exam Notes

The Root

• Underground component of a flowering plant; shoot system occurs above ground.

• Origin

  • $\text{Radicle} \rightarrow \text{primary root (tap root in dicots)}$

  • Lateral roots: secondary, tertiary, etc.

• Types of root systems (Fig. 5.2)

  • Tap-root system: single main root with laterals (e.g. mustard)

  • Fibrous root system: primary root short-lived; many roots from stem base (e.g. wheat; characteristic of monocots)

  • Adventitious roots: arise from parts other than radicle (e.g. grass, Monstera, banyan)

• Functions

  • Absorb water & minerals

  • Anchorage

  • Storage of food

  • Synthesis of growth regulators

Regions of a Root Tip

• Root cap: thimble-like, protects meristem

• Region of meristematic activity: small thin-walled cells, rapid division

• Region of elongation: cell enlargement → root length

• Region of maturation: cells differentiate; epidermal cells form root hairs (absorption)

Modifications of Roots

• Storage

  • Tap roots: carrot, turnip

  • Adventitious: sweet-potato

• Support

  • Prop roots: hanging roots of banyan (aerial, from branches)

  • Stilt roots: supporting roots from lower stem nodes of maize, sugarcane

• Respiration

  • Pneumatophores: vertical roots in swampy species (Rhizophora) for $\text{O}_2$ uptake

The Stem

• Ascending axis derived from plumule; bears nodes & internodes with axillary/terminal buds.

• Young stems: green; mature: woody/brown.

• Functions

  • Spread branches bearing leaves, flowers, fruits

  • Conduct water, minerals (xylem) & photosynthates (phloem)

  • May store food, aid in support, protection, vegetative propagation

Modifications of Stems (Fig. 5.6)

• Underground (perennation & storage): potato (tuber), ginger (rhizome), turmeric, zaminkand, Colocasia

• Tendrils (climbing): axillary, slender, coiled e.g. gourds, grapevine

• Thorns (defence): axillary buds → sharp points; Citrus, Bougainvillea

• Phylloclades/cladodes (photosynthetic, water-storage): flattened Opuntia, cylindrical Euphorbia (arid adaptations)

• Runners: long slender creeping stem of grass, strawberry → vegetative spread

• Suckers: mint, jasmine—lateral branch grows aerially then roots

• Stolons: arching lateral branch of Pistia, Eichhornia—rosettes with roots at nodes

• Offsets: banana, pineapple, Chrysanthemum—horizontal underground branches, then emerge obliquely

The Leaf

• Lateral flattened exogenous organ at node; axillary bud present.

• Origin: shoot apical meristem; acropetal arrangement.

• Primary function: photosynthesis; also transpiration, gas exchange, sometimes storage/defence.

Parts of a Typical Leaf (Fig. 5.7a)

• Leaf base (may have stipules; pulvinus swollen base in legumes)

• Petiole (stalk)

• Lamina/leaf blade (midrib, veins, veinlets)

Venation

• Reticulate: network (dicots)

• Parallel: veins run parallel (monocots)

Types of Leaves

• Simple: lamina entire or incised not reaching midrib

• Compound: incisions reach midrib → leaflets.

  • Pinnately compound: leaflets on rachis (e.g. neem)

  • Palmately compound: leaflets at petiole tip (e.g. silk-cotton)

Phyllotaxy (leaf arrangement)

• Alternate: one leaf/node alternately (china-rose, mustard, sunflower)

• Opposite: pair/node opposite (Calotropis, guava)

• Whorled: $\ge 3$ leaves/node forming whorl (Alstonia)

Leaf Modifications

• Tendrils: climbing (pea)

• Spines: defence (cactus)

• Fleshy leaves: storage (onion, garlic)

• Phyllodes: petiole expands & photosynthesises (Australian acacia)

• Insectivory: pitcher plant, Venus fly-trap

Inflorescence

• Arrangement of flowers on floral axis.

• Racemose: main axis indefinite; lateral flowers in acropetal succession (old–>young upwards)

• Cymose: main axis ends in a flower; growth limited; flowers in basipetal order (young–>old upwards)

The Flower

• Modified shoot; sexual reproductive unit.

• Four whorls on receptacle/thalamus: calyx, corolla (accessory) & androecium, gynoecium (reproductive).

Unisexual vs Bisexual

• Bisexual: both androecium & gynoecium (e.g. mustard)

• Unisexual: either stamens or carpels only

Symmetry

• Actinomorphic (radial) ⊕: multiple planes (mustard, Datura)

• Zygomorphic %: single plane (pea, Cassia)

• Asymmetric: none (canna)

Floral Series Based on Ovary Position (Fig. 5.13)

• Hypogynous: ovary superior; other whorls below (mustard, china rose, brinjal)

• Perigynous: ovary half-inferior; whorls on thalamus rim (rose, plum, peach)

• Epigynous: ovary inferior; thalamus fused around ovary; other whorls above (guava, cucumber, sunflower ray florets)

Calyx

• Sepals; usually green.

• Gamosepalous (fused) vs polysepalous (free)

Corolla

• Petals; brightly coloured.

• Gamopetalous vs polypetalous.

• Common shapes: tubular, bell, funnel, wheel.

• Aestivation (arrangement in bud) (Fig. 5.15)

  • Valvate: margins touch, no overlap (Calotropis)

  • Twisted: each overlaps next in one direction (china-rose, cotton)

  • Imbricate: overlapping irregular (Cassia, gulmohur)

  • Vexillary (papilionaceous): standard > wings > keel (pea, bean)

Androecium

• Stamens: filament + bilobed anther (pollen sacs).

• Staminode = sterile stamen.

• Attachment

  • Epipetalous: stamens on petals (brinjal)

  • Epiphyllous: on perianth (lily)

• Cohesion among stamens

  • Polyandrous: free

  • Monoadelphous: fused into 1 bundle (china-rose)

  • Diadelphous: 2 bundles (pea)

  • Polyadelphous: >2 bundles (citrus)

• Filament length variation: Salvia, mustard

Gynoecium

• Carpels: stigma + style + ovary.

• Apocarpous: free carpels (lotus, rose)

• Syncarpous: fused carpels (mustard, tomato)

• Ovary → fruit after fertilisation; ovules → seeds.

Placentation Types (Fig. 5.16)

• Marginal: along ventral suture, two rows (pea)

• Axile: on central axis in multilocular ovary (china-rose, tomato, lemon)

• Parietal: ovules on inner wall; false septum may form (mustard, Argemone)

• Free-central: on central column, no septa (Dianthus, Primrose)

• Basal: single ovule at base (sunflower, marigold)

The Fruit

• Mature/ripened ovary.

• Parthenocarpic fruit: formed without fertilisation.

• Pericarp layers when fleshy: epicarp, mesocarp, endocarp.

• Drupe (mango, coconut): monocarpellary, one-seeded.

  • Mango: thin epicarp, fleshy edible mesocarp, stony endocarp.

  • Coconut: fibrous mesocarp.

The Seed

• Post-fertilisation ovule.

• Components: seed coat (testa + tegmen) and embryo (radicle, embryonal axis, cotyledon(s)).

Dicot Seed (e.g. gram) (Fig. 5.18)

• Cotyledons two, fleshy; reserve food.

• Hilum: scar of attachment; micropyle above hilum.

• Endosperm absent in mature non-endospermic seeds (bean, pea). Present in endospermic (castor).

Monocot Seed (e.g. maize) (Fig. 5.19)

• Seed coat fused with fruit wall.

• Bulk of seed = endosperm (food store) surrounded by aleurone layer.

• Embryo: one cotyledon (scutellum) + plumule + radicle.

• Protective sheaths: coleoptile (plumule) & coleorhiza (radicle).

Semi-Technical Description & Floral Formulae

• Sequence: habit → vegetative (root, stem, leaf) → floral (inflorescence, flower) → diagram + formula.

• Symbols

  • Br = bracteate

  • $K$ = calyx, $C$ = corolla, $P$ = perianth, $A$ = androecium, $G$ = gynoecium

  • $G$ (line above) = inferior ovary; $G$ (line below) = superior

  • ⊕ actinomorphic; % zygomorphic; $\odot$ often used for bisexual

  • Fusion: ( ) cohesion; line over symbols = adhesion

• Example: mustard (Brassica) floral formula (Fig. 5.20)
  $\text{⊕ }\; K<em>{2+2}\; C</em>{4}\; A<em>{2+4}\; G</em>{(2)}$

Selected Angiosperm Families

Fabaceae (Papilionoideae)

• Habit: trees, shrubs, herbs; root nodules (N₂ fixation).

• Leaves: alternate, usually pinnately compound; stipulate; pulvinate base.

• Inflorescence: racemose.

• Flower: bisexual, zygomorphic, papilionaceous.

• Calyx $K(5)$ gamosepalous (valvate/imbricate).

• Corolla papilionaceous $C_{1+2+(2)}$ vexillary.

• Androecium diadelphous $A_{(9)+1}$.

• Gynoecium monocarpellary, ovary superior, many-ovulate; fruit legume.

• Economic uses: pulses (gram, arhar, moong), oil (soybean, groundnut), dye (Indigofera), fibre (sunhemp), fodder (Sesbania), ornamentals (lupin), medicine (mulethi).

Solanaceae (Potato family)

• Habit: herbs/shrubs; some small trees.

• Stem: often herbaceous; potato has underground tuber.

• Leaves: alternate, simple; pinnate rarely; exstipulate.

• Inflorescence: solitary axillary or cymose.

• Flower: bisexual, actinomorphic.

• Calyx $K(5)$ united, persistent.

• Corolla $C(5)$ united; valvate.

• Androecium $A5$, epipetalous.

• Gynoecium bicarpellary, syncarpous; ovary superior, bilocular, axile placentation.

• Fruit: berry/capsule; seeds many, endospermic.

• Uses: food (potato, tomato, brinjal), spice (chilli), medicines (belladonna, ashwagandha), tobacco, ornamentals (petunia).

Liliaceae (Lily family – monocot)

• Habit: perennial herbs with bulbs/corms/rhizomes.

• Leaves: mostly basal, linear; parallel venation.

• Inflorescence: solitary, cymose, often umbel.

• Flower: bisexual, actinomorphic.

• Perianth: $P(3+3)$, tepals united into tube; valvate.

• Androecium: $A_{3+3}$, epitepalous.

• Gynoecium: $G_{(3)}$ superior; tricarpellary, trilocular, axile.

• Fruit: capsule/berry; seeds endospermic.

• Uses: ornamentals (tulip, Gloriosa), medicinal (Aloe), vegetable (Asparagus), colchicine (Colchicum).

Key Takeaways

• Morphological diversity arises from adaptations for storage, support, reproduction, protection & environmental stresses.

• Root, stem, leaf show characteristic modifications diagnostic for taxonomy.

• Flower structure (symmetry, aestivation, placentation, ovary position) underpins classification.

• Semi-technical descriptions standardise terminology, aided by floral formulae & diagrams.