Morphology of Flowering Plants – Comprehensive Study Notes

Overview of Morphology of Flowering Plants

• Angiosperms share five fundamental organs: roots, stems, leaves, flowers, fruits despite exhibiting striking external diversity.
• Accurate description and classification require:
  • Standard technical vocabulary.
  • Recognition of morphological variations as ecological adaptations (e.g.
    – storage, protection, climbing, respiration in swampy habitats).
• Body divided into
  • Root system (generally subterranean).
  • Shoot system (aerial; bears leaves, buds, flowers, fruits).

Root System (Chapter 5.1)

1. Types of Root Systems

• Tap root system (dicots, e.g. mustard)
  • Primary (tap) root originates from radicle and persists.
  • Gives rise to lateral roots: secondary, tertiary …
• Fibrous root system (monocots, e.g. wheat)
  • Short-lived primary root replaced by many equal-sized adventitious roots from stem base.
• Adventitious roots
  • Develop from organs other than radicle (e.g. banyan, grasses, Monstera).

2. Regions of the Root

• Root cap – thimble-shaped protective cap over apical meristem.
• Region of meristematic activity – actively dividing cells just above cap.
• Region of elongation – cells rapidly enlarge → root lengthens.
• Region of maturation / differentiation – cells mature; some epidermal cells form root hairs (absorption of water & minerals).

3. Functions

• Absorption of water & minerals.
• Anchorage.
• Storage of reserves.
• Synthesis of plant growth regulators.

4. Modifications of Roots

• Storage – tap roots of carrot, turnip; adventitious roots of sweet-potato store food.
• Support
  • Prop / pillar roots – hanging from tree branches (banyan).
  • Stilt roots – oblique outgrowths from lower nodes (maize, sugarcane).
• Respiration – pneumatophores (Rhizophora in mangroves) grow upward to obtain $\text{O}_2$.

Stem (Chapter 5.2)

1. Diagnostic Features

• Ascending axis from plumule of embryo.
• Bears nodes (leaf attachment) and internodes.
• Contains axillary & terminal buds.
• Young stems green (photosynthetic); older stems woody/brown.
• Functions: display leaves/flowers/fruits; conduction of water, minerals, photosynthates; may store food, provide support, protection, vegetative propagation.

2. Stem Modifications

• Underground storage/perennation – potato (tuber with eyes), ginger & turmeric (rhizomes), zaminkand, Colocasia (corms).
• Stem tendrils – slender coiled structures for climbing (cucumber, pumpkins, watermelon, grapevine).
• Thorns – hard pointed axillary buds (Citrus, Bougainvillea) deter herbivory.
• Phylloclades/Cladodes – photosynthetic flattened (Opuntia) or cylindrical fleshy (Euphorbia) stems in arid plants.
• Runners/Stolons – slender stems spread horizontally; grass, strawberry (new plants at nodes after older parts die).
• Suckers – mint, jasmine: lateral branch initially aerial then roots when touching ground.
• Offsets – short horizontal internode with leaf rosette & root tuft in aquatic Pistia, Eichhornia.
• Basal underground branches – banana, pineapple, Chrysanthemum produce leafy shoots obliquely upward.

Leaf (Chapter 5.3)

1. Parts of a Typical Leaf

• Leaf base – may form sheath (monocots) or swollen pulvinus (legumes).
• Petiole – stalk positioning blade for light; flexibility causes fluttering → cooling & fresh air.
• Lamina (blade) – flat green surface; contains midrib, veins, veinlets.
  • Veins provide mechanical strength & transport pathways.
• May possess stipules (lateral appendages) at leaf base.

2. Venation

• Reticulate – network pattern (most dicots).
• Parallel – veins run parallel (most monocots).

3. Leaf Types

• Simple leaf – lamina entire or incisions not reaching midrib.
• Compound leaf – incisions reach midrib; leaflets possess no axillary bud.
  • Pinnately compound – leaflets on rachis (e.g. neem).
  • Palmately compound – leaflets radiate from tip of petiole (silk cotton).

4. Phyllotaxy (Leaf Arrangement)

• Alternate – one leaf per node in spiral sequence (china rose, mustard, sunflower).
• Opposite – two leaves/node opposite (guava, Calotropis).
• Whorled – $\ge 3$ leaves/node forming circle (Alstonia).

5. Leaf Modifications

• Tendrils – climbing (pea).
• Spines – defence, reduce transpiration (cactus).
• Storage leaves – thick fleshy (onion, garlic).
• Phyllodes – petioles become photosynthetic after lamina reduction (Australian Acacia).
• Insectivorous traps – pitcher plant, Venus fly-trap.

Inflorescence (Chapter 5.4)

• Definition: arrangement of flowers on the floral axis.
• Two principal types based on growth of main axis:
  • Racemose – axis continues to grow; flowers in acropetal (older → younger) order. Example structures: raceme, spike, panicle, catkin etc.
  • Cymose – axis ends in a flower; limited growth; flowers in basipetal (younger → older) order. Types: monochasial, dichasial, polychasial cymes.

Flower (Chapter 5.5)

1. General Plan

• Modified condensed shoot; internodes shortened; floral appendages on thalamus/receptacle.
• Four whorls (outer → inner): calyx, corolla, androecium, gynoecium.
  • Calyx & corolla = accessory.
  • Androecium & gynoecium = reproductive.
• Bisexual (both whorls) vs unisexual (only one).
• Symmetry:
  • Actinomorphic (radial) – multiple planes of division (mustard, datura, chilli).
  • Zygomorphic (bilateral) – single plane (pea, gulmohur, Cassia).
  • Asymmetric – no plane (canna).
• Merosity – trimerous, tetramerous, pentamerous (multiples of $3,4,5$).
• Bracteate vs ebracteate (presence/absence of subtending bract).

2. Position of Ovary on Thalamus

• Hypogynous – gynoecium highest; ovary superior (mustard, china rose).
• Perigynous – floral parts at same level on cup-shaped thalamus; ovary half-inferior (rose, plum, peach).
• Epigynous – thalamus encloses ovary; other parts above; ovary inferior (guava, cucumber, sunflower ray florets).

3. Calyx (Sepals)

• Usually green; protection during bud stage.
• Gamosepalous (united) vs polysepalous (free).

4. Corolla (Petals)

• Brightly coloured – pollinator attraction.
• Shapes: tubular, bell, funnel, wheel.
• Gamopetalous vs polypetalous.

Aestivation (arrangement in bud)

1. Valvate – margins just touch (Calotropis).
2. Twisted – each overlaps next (china-rose, okra, cotton).
3. Imbricate – overlapping irregular (Cassia, gulmohur).
4. Vexillary/Papilionaceous – standard → wings → keel (pea, bean).

5. Androecium (Stamens)

• Parts: filament + anther (bilobed, tetrasporangiate; forms pollen).
• Staminode – sterile stamen.
• Adhesion to other whorls:
  • Epipetalous (to petals; brinjal).
  • Epiphyllous (to perianth; lily).
• Cohesion among stamens:
  • Polyandrous – free.
  • Monadelphous – fused into one bundle (china-rose).
  • Diadelphous – two bundles $9+1$ (pea).
  • Polyadelphous – many bundles (citrus).
• Filament length variation: e.g. Salvia, mustard.

6. Gynoecium (Carpels)

• Components: ovary, style, stigma.
• Apocarpous – free carpels (lotus, rose).
• Syncarpous – fused carpels (mustard, tomato).
• Post-fertilisation: ovary → fruit; ovules → seeds.

Placentation (Arrangement of Ovules)

• Marginal – along ventral suture, two rows (pea).
• Axile – placenta central with septa; multilocular (china-rose, tomato, lemon).
• Parietal – inner wall; false septa create two chambers (mustard, Argemone).
• Free-central – on central column without septa (Dianthus, Primrose).
• Basal – placenta at base; single ovule (sunflower, marigold).

Fruit (Chapter 5.6)

• Definition – mature/ripened ovary after fertilisation.
• Parthenocarpic fruit – develops without fertilisation (seedless).
• Pericarp (fruit wall) may be dry/fleshy; if thick fleshy, differentiated into epicarp, mesocarp, endocarp.
• Drupe – one-seeded, from monocarpellary superior ovary (mango, coconut).
  • Mango: thin epicarp, edible fleshy mesocarp, stony endocarp.
  • Coconut: fibrous mesocarp.

Seed (Chapter 5.7)

1. Dicotyledonous Seed (e.g. gram, pea)

• Seed coat – outer testa, inner tegmen; has hilum (attachment scar) & micropyle (minute pore).
• Embryo = embryonal axis + two fleshy cotyledons (reserve food).
  • Axis ends: radicle (embryonic root), plumule (embryonic shoot).
• Endosperm may be persistent (endospermic e.g. castor) or consumed (non-endospermic e.g. pea).

2. Monocotyledonous Seed (e.g. maize)

• Seed coat fused with thin fruit wall.
• Massive endosperm (food) surrounded by protein-rich aleurone layer.
• Embryo small, at one end:
  • Single cotyledon = scutellum.
  • Axis bears plumule (protected by coleoptile) and radicle (protected by coleorhiza).
• Usually endospermic; orchids exceptional (non-endospermic).

Semi-technical Description & Floral Formulae (Chapter 5.8)

• Sequence: habit → root → stem → leaf → inflorescence → flower.
• Symbols in floral formula:
  • $\text{Br}$ bracteate; $\text{EBr}$ ebracteate.
  • $\text{K}$ calyx, $\text{C}$ corolla, $\text{P}$ perianth, $\text{A}$ androecium, $\text{G}$ gynoecium.
  • Overbar $\bar{G}$ or underline $\underline{G}$ indicates inferior ovary; plain $G$ superior.
  • $\bigcirc$ (⊕) actinomorphic; % (or $\%$) zygomorphic.
  • \male,\female for unisexual; $\bigotimes$ or $\leftrightarrow$ for bisexual.
  • ( ) fusion (cohesion); line above for adhesion.
• Example – Mustard (Brassicaceae) floral formula: $\oplus K\,2+2\; C\,4\; A\,2+4\; G\,(2)$

Representative Angiosperm Families (Chapter 5.9)

1. Fabaceae (Papilionoideae)

• Habit: herb/shrub/tree with root nodules (N-fixation).
• Leaves: alternate, pinnately compound; pulvinus; stipulate.
• Inflorescence: racemose.
• Flower: bisexual, zygomorphic.
• Corolla: papilionaceous (standard, wings, keel).
• Androecium: $9+1$ diadelphous; anthers dithecous.
• Gynoecium: monocarpellary, many-ovulate; superior ovary.
• Fruit: legume; seeds non-endospermic.
• Uses: pulses (gram, moong), oils (soybean, groundnut), dyes (Indigofera), fibre (sunhemp), fodder (Trifolium), ornamentals, medicines.

2. Solanaceae (Potato family)

• Habit: herbs/shrubs, rarely trees; e.g. Solanum, Capsicum, Nicotiana.
• Leaves: alternate, simple; often hairy; exstipulate.
• Flowers: bisexual, actinomorphic; solitary axillary or cymose.
• Calyx: $K(5)$ persistent.
• Corolla: $C(5)$ gamopetalous; valvate.
• Androecium: $A5$ epipetalous.
• Gynoecium: $G\,(2)$ bicarpellary, syncarpous; axile placentation; superior ovary.
• Fruit: berry (tomato) or capsule.
• Seeds: many, endospermous.
• Uses: food (potato, tomato, brinjal), spices (chilli), medicine (belladonna, ashwagandha), tobacco, ornamentals (Petunia).

3. Liliaceae (Lily family – monocots)

• Habit: perennial herbs with bulbs/corms/rhizomes.
• Leaves: mostly basal, linear, parallel venation.
• Inflorescence: solitary/cyme, often umbellate.
• Perianth: $P(3+3)$ petaloid tepals forming tube.
• Androecium: $A3+3$ epitepalous.
• Gynoecium: $G\,(3)$ trilocular, axile placentation.
• Fruit: capsule; seeds endospermous.
• Uses: ornamentals (tulip, Gloriosa), medicinal (Aloe), vegetable (Asparagus), source of colchicine (Colchicum).

Conceptual & Real-world Connections

• Morphological adaptations illustrate structure–function relationships and evolutionary pressures (e.g. pneumatophores in hypoxic soils; phylloclades in xerophytes).
• Root nodules (Fabaceae) exemplify plant–microbe symbiosis for nitrogen fixation → agricultural importance.
• Persistent calyx (Solanaceae) protects developing fruit; illustrates protective morphology.
• Underground stems (potato) show that positional context (below soil) isn’t a definitive criterion; developmental origin matters.
• Knowledge of floral formulae & diagrams underpins taxonomy, phylogeny, breeding, forensic botany.

Representative Numerical / Formulae References

• Floral part multiples: $3,4,5$ define trimerous, tetramerous, pentamerous.
• Diadelphous condition in pea written $A(9)+1$.
• Mustard floral formula $\oplus K\,2+2\; C\,4\; A\,2+4\; G\,(2)$ encapsulates entire description in one line.

Exercise & Revision Highlights

• Distinguish between
  • Tap, fibrous, adventitious roots.
  • Racemose vs cymose inflorescence.
  • Apocarpous vs syncarpous ovary.
• Draw & label: dicot seed (gram); vertical section of monocot seed (maize).
• Practice semi-technical descriptions for Fabaceae & Solanaceae specimens.
• Memorise definitions: aestivation, placentation, actinomorphic, zygomorphic, hypogynous, perigynous, epipetalous.
• Example application question: provide floral formula for actinomorphic, bisexual, hypogynous flower with $K(5), C5, A5, G\,(2)$ and axile placentation ⇒ $\oplus K\,(5)\; C5\; A5\; G\,(2)$.

Ethical, Philosophical, Practical Implications

• Understanding plant morphology guides crop improvement, conservation, and sustainable agriculture.
• Recognition of medicinally valuable families (e.g. Solanaceae alkaloids, Liliaceae phytochemicals) raises questions on bioprospecting & biodiversity ethics.
• Structural modifications (thorns, toxins) reflect plant defence strategies – metaphors for adaptation & resilience in biological systems.