Morphology of Flowering Plants

🎯 Key Points

• Root tip zones (tip to base): root cap → meristematic → elongation → maturation (root hair) zone
• Stem modifications: rhizome (ginger), tuber (potato), bulb (onion), corm (colocasia) - all underground but only roots have root caps/root hairs, helping distinguish modified stems from roots
• Dicot stem: vascular bundles in a RING, cambium present (open, secondary growth possible); Monocot stem: bundles SCATTERED, no cambium (closed, no secondary growth)
• Dicot leaf: dorsiventral, palisade+spongy mesophyll, stomata mainly on lower surface; Monocot leaf: isobilateral, undifferentiated mesophyll, stomata on both surfaces
• Dicot root: few xylem bundles (2-6); Monocot root: many xylem bundles (polyarch, 6+) and a large well-developed pith
• Secondary growth: vascular cambium → secondary xylem/phloem; cork cambium (phellogen) → bark; annual rings used for dendrochronology (tree age estimation)

Root System

• Tap root: primary root with lateral branches (dicots); e.g., carrot, radish
• Fibrous root: many roots of similar size (monocots); e.g., grass, wheat
• Modifications: storage (carrot), breathing roots/pneumatophores (Avicennia), prop roots (banyan), stilt roots (maize)
• Root tip regions: root cap → meristematic zone → elongation zone → maturation zone (root hair zone)

Stem

• Conducts water and nutrients; supports leaves; site of photosynthesis (green stems)
• Modifications: rhizome (ginger), tuber (potato - swollen stem), bulb (onion), corm (colocasia), stem tendrils (grapevine), thorn (Bougainvillea), phylloclade (Opuntia)

Leaf

• Lamina (blade), petiole, leaf base; stipules may be present
• Venation: parallel (monocots), reticulate (dicots)
• Simple leaf: single undivided lamina; Compound leaf: divided into leaflets
• Phyllotaxy: arrangement of leaves on stem (alternate, opposite, whorled)
• Leaf modifications: tendrils (Pisum), spines (Opuntia/cactus), pitcher (Nepenthes/insectivorous)

Plant Tissues

• Meristematic tissue: dividing cells; apical (tip growth), lateral (girth), intercalary (between nodes)
• Permanent tissues: Simple (parenchyma, collenchyma, sclerenchyma) and Complex (xylem, phloem)
• Parenchyma: living, thin-walled, storage and packing
• Collenchyma: support in young growing plants
• Sclerenchyma: dead, thick walls, support (fibres and sclereids)
• Xylem: water transport (vessels, tracheids, fibres, parenchyma)
• Phloem: food transport (sieve tubes, companion cells, fibres, parenchyma)

Dicot vs Monocot Stem (anatomy)

• Dicot stem: vascular bundles in ring; open (cambium present); secondary growth possible
• Monocot stem: vascular bundles scattered; closed (no cambium); no secondary growth

Types of Inflorescence

• Racemose: the main floral axis continues to grow and produces flowers laterally in acropetal succession (older flowers toward the base, younger toward the tip); examples include raceme (mustard), spike (Adhatoda), and umbel (coriander)
• Cymose: the main axis terminates in a flower early, so growth and branching continue laterally below it; flowers are arranged in basipetal order (younger flowers toward the base); seen in cymes and verticillasters (Ocimum)

Anatomy: Dicot vs Monocot Leaf and Root

• Dicot leaf: dorsiventral (bifacial), with distinct upper and lower surfaces; mesophyll differentiated into palisade (upper, columnar, more chloroplasts) and spongy parenchyma (lower, irregular, air spaces); stomata mainly on the lower surface
• Monocot leaf: isobilateral, mesophyll not differentiated into palisade and spongy layers; stomata present on both surfaces; bulliform cells present in some grasses to help leaf rolling during water stress
• Dicot root: limited xylem bundles (usually 2 to 6, polyarch is rare), cambium develops later for secondary growth, pith small or absent
• Monocot root: many xylem bundles (polyarch, 6 or more), no cambium, large well-developed pith present

Secondary Growth

• Increase in girth of stems and roots due to activity of cambium (vascular cambium forms secondary xylem and phloem; cork cambium/phellogen forms the outer bark)
• Annual rings: alternating layers of spring wood (large vessels, lighter) and autumn wood (smaller vessels, darker) formed due to seasonal variation in cambium activity; used to estimate the age of a tree (dendrochronology)
• Heartwood (dark, non-conducting, resistant to decay) versus sapwood (lighter, peripheral, active in water conduction)

The Flower: Parts and Symmetry

• A flower is a modified shoot; the four whorls (outer to inner) are calyx (sepals, protective), corolla (petals, attract pollinators), androecium (stamens, male), and gynoecium (carpels/pistil, female)
• Symmetry: actinomorphic (radial - can be cut into equal halves along any plane, e.g. mustard, Datura); zygomorphic (bilateral - only one plane of symmetry, e.g. pea, Cassia)
• Number of parts: trimerous, tetramerous, or pentamerous (floral parts in multiples of 3, 4, or 5); monocots are typically trimerous, dicots tetra- or pentamerous
• Position of ovary vs other whorls: hypogynous (superior ovary, other parts below - mustard, china rose); perigynous (half-inferior ovary, parts at the same level - rose, plum); epigynous (inferior ovary, other parts above - guava, cucumber, sunflower)
• A complete flower has all four whorls; a bisexual flower bears both androecium and gynoecium, a unisexual flower only one

Aestivation and Placentation

• Aestivation (arrangement of sepals or petals in a floral bud): valvate (margins just touch, no overlap - Calotropis); twisted/contorted (one margin regularly overlaps the next - china rose, cotton); imbricate (overlapping without a definite direction - Cassia, gulmohar); vexillary/papilionaceous (a large standard covers two wings, which cover two keel petals - pea, bean)
• Placentation (arrangement of ovules within the ovary): marginal (ovules on one ridge - pea); axile (ovules on a central axis in a chambered ovary - china rose, tomato, lemon); parietal (ovules on the inner ovary wall - mustard, Argemone); free central (ovules on a central axis with no septa - Dianthus, Primrose); basal (a single ovule at the ovary base - sunflower, marigold)

Types of Fruits

• A fruit is the mature, ripened ovary formed after fertilisation; the ovary wall becomes the pericarp, which may be dry or fleshy
• True fruit develops only from the ovary (mango); false fruit has other floral parts contributing to it (apple - the fleshy edible part is the thalamus)
• Drupe: a fleshy fruit with a hard stony endocarp around the seed (mango, coconut, almond); in a berry the seeds are embedded in fleshy pulp (tomato, grape)
• Parthenocarpic fruit: develops from the ovary without fertilisation and is therefore seedless (banana)

Seed Structure: Dicot vs Monocot

• The hilum is the scar where the seed was attached to the fruit; the micropyle is a small pore just above the hilum through which water is absorbed during germination

Floral Formula and Important Families

• Fabaceae (Papilionaceae, the pea family): zygomorphic bisexual flower; calyx 5 (fused), corolla 5 (papilionaceous - 1 standard, 2 wings, 2 keel), androecium 10 (diadelphous - 9 fused + 1 free), gynoecium 1 (superior, monocarpellary, marginal placentation); fruit a legume; examples pea, gram, groundnut; economically vital as pulses and for nitrogen fixation
• Solanaceae (the potato/nightshade family): actinomorphic bisexual; calyx 5 (fused, persistent), corolla 5 (fused), androecium 5 (epipetalous), gynoecium 2 (fused, superior, axile placentation, ovary obliquely placed); fruit a berry or capsule; examples potato, tomato, brinjal, tobacco, Datura
• Liliaceae (the lily family, a monocot): actinomorphic bisexual and trimerous; perianth of 6 tepals (3 + 3, often fused), androecium 6, gynoecium 3 (fused, superior, axile placentation); examples lily, onion, garlic, Aloe, tulip

🚀 NEET Advanced Edge

Distinguishing a modified stem from a root by clue words: If the structure has "nodes, internodes, scale leaves, or axillary buds" → it's a modified STEM (e.g. potato tuber has "eyes" which are axillary buds); if it lacks these and instead has a root cap → it's a true root (e.g. sweet potato, a root modification, NOT a stem tuber).

Why bulliform cells matter: In grasses (monocot leaves), bulliform cells on the upper epidermis lose turgor under water stress, causing the leaf to roll/fold inward - reducing the exposed surface area and transpiration rate, a structural drought-avoidance adaptation often tested alongside stomatal closure.

Reading a transverse section (T.S.) in an exam image: A T.S. showing scattered vascular bundles with no visible cambium ring → monocot stem. A T.S. showing bundles arranged in a ring WITH a continuous cambium layer → dicot stem. Polyarch xylem (6+ groups) arranged around a large pith → monocot root.

Modifications of Roots

• Storage roots: tap roots swell for food storage as in carrot and turnip; adventitious roots swell as in sweet potato.
• Prop roots: pillar-like supporting roots hanging from branches of the banyan tree.
• Stilt roots: supporting roots arising from lower nodes of the stem in maize and sugarcane.
• Pneumatophores: roots that grow vertically upward for gaseous exchange in marshy mangroves like Rhizophora.
• Roots of some plants are modified for nitrogen fixation (nodules) or become respiratory in swampy habitats.

Modifications of Stem

• Underground stems for storage and perennation: rhizome (ginger), tuber (potato with eyes as nodes), corm (Colocasia), bulb (onion).
• Stem tendrils: slender, spirally coiled, help climbing as in gourds and grapevine; they arise from axillary buds.
• Thorns: woody, pointed axillary stem modifications for protection as in Citrus and Bougainvillea.
• Phylloclade: flattened or cylindrical green photosynthetic stem in xerophytes like Opuntia and Euphorbia.
• Offset (water hyacinth) and runner (grasses) are sub-aerial stems for vegetative propagation.

Modifications of Leaves

• Tendrils: leaves or leaflets modified into slender coiling structures for climbing as in peas.
• Spines: leaves reduced to spines to reduce water loss and for defence as in cacti and Opuntia.
• Storage leaves: fleshy scale leaves of onion and garlic store food and water.
• Pitcher and bladder: leaves of insectivorous plants like Nepenthes and Utricularia trap insects.
• Phyllode: petiole expands into a green photosynthetic structure in Australian Acacia.

Venation, Phyllotaxy and Leaf Types

• Venation: reticulate (net-like, typical of dicots) versus parallel (typical of monocots).
• Simple leaf: lamina is entire or incised but not up to the midrib; compound leaf: lamina divided into leaflets up to the midrib.
• Pinnately compound (neem) has leaflets on a common rachis; palmately compound (silk cotton) has leaflets attached at a common point.
• Phyllotaxy is the pattern of leaf arrangement: alternate (China rose), opposite (Calotropis), whorled (Alstonia).
• An axillary bud is present in the axil of a leaf; this helps distinguish a leaf from a leaflet, which has no bud.