Morphology of Flowering Plants – Comprehensive Study Notes

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Overview of Plant Morphology

• Flowering (angiosperm) plants display vast external diversity yet share five universal organs: roots, stems, leaves, flowers and fruits.
• Accurate classification demands standard terminology & definitions plus awareness of organ variations that reflect environmental adaptations (e.g.
  • Habitat-specific adjustments
  • Protective structures
  • Climbing aids
  • Storage tissues)
• A typical flowering plant is divided into
  • Root system – subterranean
  • Shoot system – aerial (Figure $5.1$ reference)

The Root (Section $5.1$)

• In most dicots, direct elongation of the radicle ➜ primary root ➜ gives rise to lateral roots of successive orders (secondary, tertiary …). All branches $+$ primary root = tap-root system (e.g., mustard).
• In monocots, primary root is short-lived; many roots arise from stem base ➜ fibrous root system (e.g., wheat).
• Roots arising from any organ other than the radicle are adventitious roots (e.g., grass, Monstera, banyan).
• Core functions: water–mineral absorption, anchorage, food storage, synthesis of growth regulators.

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Major Root Types (Fig. $5.2$)

$\bullet$ Tap root
$\bullet$ Fibrous root
$\bullet$ Adventitious root

Functional Review

• Tap-root system prominent in dicots (mustard).
• Fibrous roots dominate monocots (wheat).
• Adventitious roots perform specialised tasks (e.g., banyan prop roots).

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Regions of a Root (Section $5.1.1$) – Fig. $5.3$

$1.$ Root cap – thimble-like; shields apical meristem while penetrating soil.
$2.$ Region of meristematic activity – tiny, thin-walled, densely cytoplasmic cells; active mitosis.
$3.$ Region of elongation – cells enlarge lengthwise ➜ root elongation.
$4.$ Region of maturation – cells differentiate; some epidermal cells protrude as root hairs (absorption sites).

Root Modifications (Section $5.1.2$)

• Storage: Swollen tap roots (carrot, turnip) & swollen adventitious roots (sweet potato).
• Support: Prop roots (banyan) descend from branches; stilt roots (maize, sugarcane) emerge from lower nodes.
• Respiration: Pneumatophores in mangroves (Rhizophora) grow upward, funnel $O_2$ to submerged roots.

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The Stem (Section $5.2$)

• Ascending axis; originates from plumule.
• Has nodes (leaf attachment) & internodes (segments between nodes).
• Bears terminal & axillary buds; green & photosynthetic when young; often woody later.
• Primary roles: expose leaves/flowers/fruits, conduct water/minerals/photosynthates.
• Secondary roles: storage, support, protection, vegetative propagation.

Stem Modifications (Section $5.2.1$) – Fig. $5.6$

• Underground storage/perennation: potato (tuber), ginger (rhizome), turmeric, Zaminkand, Colocasia.
• Stem tendrils (axillary) – slim, spiral; climbing aid in gourds & grapevine.
• Thorns (modified axillary buds) – woody, sharp; defence in Citrus, Bougainvillea.
• Phylloclades/cladodes – photosynthetic stems in arid taxa: flattened (Opuntia) or cylindrical (Euphorbia).
• Runners/Stolons – surface or underground lateral stems facilitating vegetative spread (grass, strawberry, mint, jasmine).
• Offsets – short internodes, each node with leaf rosette $+$ roots (aquatics: Pistia, Eichhornia).
• Suckers – lateral branches from subterranean stem; rise obliquely (banana, pineapple, chrysanthemum).

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The Leaf (Section $5.3$)

• Lateral, flattened organ at node; bears axillary bud; develops acropetally.
• Crucial for photosynthesis.

Parts of a Typical Leaf – Fig. $5.7a$

$\boxed{\text{Leaf base}}$ – attaches leaf; may form sheath (monocots) or pulvinus (legumes).

$\boxed{\text{Petiole}}$ – stalk; positions lamina for light, enables fluttering.

$\boxed{\text{Lamina (blade)}}$ – expanded green portion; contains midrib, veins  veinlets (rigidity $+$ transport).

• Stipules – lateral appendages (present in many dicots).

Venation (Section $5.3.1$)

• Reticulate – web-like; typical of dicots.
• Parallel – veins run side-by-side; hallmark of monocots.

Types of Leaves (Section $5.3.2$)

• Simple – lamina entire/incised but cuts don’t reach midrib.
• Compound – incisions reach midrib ➜ separate leaflets. Axillary bud is at petiole base only.
  • Pinnate – leaflets along rachis (e.g., neem).
  • Palmate – leaflets radiate from one point (e.g., silk cotton).

Phyllotaxy (Section $5.3.3$) – Fig. $5.9$

$1.$ Alternate – one leaf/node (china rose, mustard, sunflower).
$2.$ Opposite – pair/node (guava, Calotropis).
$3.$ Whorled – $\ge 3$ leaves/node (Alstonia).

Leaf Modifications (Section $5.3.4$)

• Tendrils – climbing (Pisum).
• Spines – defence (cacti).
• Fleshy leaves – storage (onion, garlic).
• Phyllodes – petiole becomes leaf-like (Australian acacia).
• Insectivorous traps – pitcher plant, venus fly-trap.

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Inflorescence (Section $5.4$)

• Arrangement of flowers on floral axis.
• Two principal types:
  • Racemose – main axis grows indefinitely; flowers in acropetal order (Fig. $5.11$).
  • Cymose – main axis ends in flower; limited growth; flowers in basipetal order (Fig. $5.12$).

The Flower (Section $5.5$)

• Reproductive shoot; four concentric whorls on thalamus/receptacle: calyx, corolla (accessory) + androecium, gynoecium (reproductive).
• Bisexual – both sex whorls; unisexual – one.
• Symmetry:
  • Actinomorphic (radial) – divisible into equal halves through any radial plane (mustard, datura).
  • Zygomorphic (bilateral) – only one vertical plane (pea, gulmohur).
  • Asymmetric – none (canna).
• Merosity: trimerous, tetramerous, pentamerous ➜ parts in $3,4,5$ multiples.
• Bracteate vs ebracteate.

Position of Ovary (Fig. $5.13$)

• Hypogynous – ovary superior (mustard, china rose).
• Perigynous – ovary half-inferior (rose, plum).
• Epigynous – ovary inferior (guava, cucumber, sunflower ray floret).

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Detailed Floral Whorls (Section $5.5.1$)

Calyx

• Sepals; green; protect bud.
• Gamosepalous (fused) vs polysepalous (free).

Corolla

• Petals; often colourful.
• Gamopetalous vs polypetalous.
• Shapes: tubular, bell, funnel, wheel.
• Aestivation (arrangement in bud) – Fig. $5.15$:
  • Valvate – margins just touch (Calotropis).
  • Twisted – each overlaps next (china rose, okra).
  • Imbricate – irregular overlap (Cassia, gulmohur).
  • Vexillary/Papilionaceous – standard > wings > keel (pea, bean).

Androecium

• Stamens = filament $+$ bilobed anther (pollen sacs).
• Sterile stamen = staminode.
• Attachment:
  • Epipetalous (to petals) – brinjal.
  • Epiphyllous (to perianth) – lily.
• Cohesion among stamens:
  • Monoadelphous (one bundle) – china rose.
  • Diadelphous (two bundles) – pea.
  • Polyadelphous (many) – citrus.
• Variation in filament length (Salvia, mustard).

Gynoecium

• Units = carpels (stigma $+$ style $+$ ovary).
• Carpels free = apocarpous (lotus, rose); fused = syncarpous (mustard, tomato).
• Ovules attach to placenta; post-fertilisation: ovary ➜ fruit, ovule ➜ seed.

Placentation Types (Fig. $5.16$)

$\bullet$ Marginal – along ventral suture; two rows (pea).
$\bullet$ Axile – central column in multilocular ovary (china rose, tomato, lemon).
$\bullet$ Parietal – inner ovary wall; false septum may appear (mustard, Argemone).
$\bullet$ Free-central – ovules on central column; no septa (Dianthus, primrose).
$\bullet$ Basal – placenta at base; single ovule (sunflower, marigold).

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The Fruit (Section $5.6$)

• Mature/ripened ovary.
• Parthenocarpic fruit develops without fertilisation.
• Wall = pericarp (may be dry/fleshy). Thick fleshy pericarp ➜ layers:
  • Epicarp – outer
  • Mesocarp – middle
  • Endocarp – inner
• Drupe (mango, coconut): monocarpellary, $1$-seeded.
  • Mango – thin epicarp, fleshy edible mesocarp, stony endocarp.
  • Coconut – fibrous mesocarp.

The Seed (Section $5.7$)

Dicot Seed Structure – Fig. $5.18$

• Seed coat = testa (outer) $+$ tegmen (inner).
• Hilum – scar of funiculus; micropyle – minute pore.
• Embryo: radicle, plumule, embryonal axis & $2$ cotyledons (food-laden).
• Endospermic (e.g., castor) vs non-endospermic (pea, gram).

Monocot Seed (Cereal) – Fig. $5.19$

• Seed coat fused with fruit wall.
• Massive endosperm ➜ aleurone layer (protein) separates embryo.
• Embryo: single scutellum (cotyledon), plumule within coleoptile, radicle within coleorhiza.
• Usually endospermic; orchids are exceptions.

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Semi-Technical Description of a Flowering Plant (Section $5.8$)

• Sequence: Habit → Roots → Stem → Leaves → Inflorescence → Flower (whorls).
• Symbols for floral formula:
  • $Br$ bracteate $K$ calyx $C$ corolla $P$ perianth $A$ androecium $G$ gynoecium.
  • Position of ovary: $\underline{G}$ (superior), $\overline{G}$ (inferior).
  • Sex: \male, \female, \bisexual.
  • Symmetry: $\oplus$ (actinomorphic), \percent (zygomorphic).
  • Fusion (cohesion) – parts in brackets; adhesion – line above symbols.
• Floral diagram shows mother-axis (dot) at top, whorls concentrically.
• Example diagram & formula given for mustard: $\oplus\;K<em>{2+2}\;C</em>{4}\;A<em>{2+4}\;\underline{G}</em>{(2)}$.

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Family Fabaceae (Section $5.9.1$)

Key Features

• Habit: trees/shrubs/herbs; roots bear Rhizobium nodules.
• Leaves: alternate, pinnate/simple; pulvinus leaf base; stipulate; reticulate venation.

Floral Details

• Inflorescence racemose.
• Flower: bisexual, zygomorphic.
• Calyx: $5$ fused sepals; valvate/imbricate.
• Corolla: $5$ free petals; papilionaceous (standard > wings > keel).
• Androecium: $10$ stamens; diadelphous ($9+1$) ; dithecous anthers.
• Gynoecium: monocarpellary; superior ovary, many ovules.
• Fruit: legume; seeds non-endospermic.
• Floral formula: $\%\;K<em>{(5)}\;C</em>{1+2+(2)}\;A<em>{(9)+1}\;G</em>1$.

Economic Role

Pulses (gram, arhar, moong, soyabean), oils (groundnut), dye (Indigofera), fibre (sunhemp), fodder, ornamentals (lupin, sweet pea), medicines (mulethi).

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Family Solanaceae (Section $5.9.2$)

Vegetative Traits

• Herbs/shrubs (rare trees). Stem herbaceous or woody; may be hollow; potato has underground stolon.
• Leaves: alternate, simple (rarely pinnate), exstipulate; reticulate venation.

Floral Profile

• Inflorescence: solitary axillary or cymose.
• Flower: bisexual, actinomorphic.
• Calyx: $5$ fused persistent sepals.
• Corolla: $5$ fused petals (rotate/tubular); valvate aestivation.
• Androecium: $5$ epipetalous stamens.
• Gynoecium: bicarpellary, syncarpous; superior bilocular ovary, axile placentation, many ovules.
• Fruit: berry/capsule; seeds many & endospermic.
• Floral formula: $\oplus\;K<em>{(5)}\;C</em>{(5)}\;A<em>5\;G</em>{(2)}$ (superior indicated elsewhere).

Uses

Food (potato, tomato, brinjal), spices (chilli), medicines (belladonna, ashwagandha), tobacco, ornamentals (petunia).

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Family Liliaceae (Section $5.9.3$)

General Characters

• Perennial monocot herbs with bulbs/corms/rhizomes.
• Leaves: mostly basal, linear, exstipulate, parallel venation.

Floral Data

• Inflorescence: solitary/cymose, often umbel.
• Flower: bisexual, actinomorphic.
• Perianth: $3+3$ tepals; often united into tube; valvate.
• Androecium: $3+3$ stamens, epitepalous.
• Gynoecium: tricarpellary, syncarpous; superior trilocular ovary; axile placentation.
• Fruit: capsule (rare berry); seeds endospermic.
• Floral formula: $Br\;\oplus\;P<em>{(3+3)}\;A</em>{3+3}\;G_{(3)}$.

Economic Value

Ornamentals (tulip, Gloriosa), drugs (Aloe), vegetable (asparagus), colchicine source (Colchicum).

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Summary Highlights

• Flowering plants’ organs experience morphological modification for storage, support, protection, reproduction & survival.
• Root: tap vs fibrous; specialised for food, support, respiration.
• Stem: recognisable via nodes/internodes; modifications (tubers, rhizomes, tendrils, thorns, runners, etc.).
• Leaf: diversity in form; specialised phyllotaxy, compound/simple types; modifications (tendrils, spines, storage, phyllodes, traps).
• Inflorescence: racemose vs cymose.
• Flower: evaluation via symmetry, sexuality, ovary position, aestivation, placentation.
• Post-fertilisation: ovary ➜ fruit; ovule ➜ seed (dicot/monocot architecture).
• Floral diagrams & formulae condense floral traits for taxonomy; demonstrated with Brassicaceae example.
• Detailed semi-technical descriptors provided for Fabaceae, Solanaceae, Liliaceae linking structure to economic importance.