Morphology of Flowering Plants

The One Thing

The morphology of flowering plants links the structure and arrangement of roots, stems, leaves, flowers, fruits, and seeds to their functions, adaptations, reproduction, and identification. External features also provide important distinctions between monocots and dicots and assist in plant classification.

Reactions, Processes and Experiments

Key Terms

• Root system: The underground part of a plant that usually anchors the plant, absorbs water and minerals, and may store food.
• Tap root system: A root system with one prominent primary root and smaller lateral roots, commonly found in dicot plants.
• Fibrous root system: A cluster of thin roots arising from the base of the stem, commonly found in monocot plants.
• Adventitious roots: Roots that arise from plant parts other than the radicle, such as stems or leaves.
• Root cap: A protective structure covering the root tip and helping it push through soil.
• Root zones: Regions of a young root arranged from the tip upward as root cap, meristematic zone, zone of elongation, and zone of maturation.
• Root modifications: Specialised roots adapted for storage, support, respiration, or climbing, including storage roots in carrot, prop roots in banyan, and pneumatophores in mangroves.
• Stem: The ascending plant axis bearing nodes, internodes, leaves, branches, flowers, and fruits.
• Node: A point on the stem from which leaves, branches, or buds arise.
• Internode: The portion of a stem between two successive nodes.
• Stem modifications: Specialised stems adapted for storage, protection, vegetative propagation, or photosynthesis, including rhizomes, tubers, bulbs, tendrils, and thorns.
• Leaf: A usually green, flattened lateral organ that performs photosynthesis, gaseous exchange, and transpiration.
• Leaf parts: A typical leaf consists of a leaf base, petiole, and lamina; stipules may occur at the leaf base.
• Venation: The arrangement of veins and veinlets in the leaf lamina; it is usually reticulate in dicots and parallel in monocots.
• Phyllotaxy: The arrangement of leaves on the stem, commonly alternate, opposite, or whorled.
• Simple leaf: A leaf with an undivided lamina, although the lamina may be deeply lobed.
• Compound leaf: A leaf whose lamina is divided into distinct leaflets; axillary buds occur at the base of the whole leaf, not at leaflet bases.
• Leaf modifications: Specialised leaves adapted for protection, climbing, storage, or insect capture, including spines, tendrils, fleshy leaves, and insectivorous leaves.
• Inflorescence: The arrangement of flowers on the floral axis.
• Racemose inflorescence: An inflorescence in which the main axis continues to grow and flowers generally develop in acropetal order.
• Cymose inflorescence: An inflorescence in which the main axis ends in a flower and flowers generally develop in basipetal order.
• Flower: A modified reproductive shoot of angiosperms that bears floral parts and participates in sexual reproduction.
• Complete flower: A flower containing all four whorls: calyx, corolla, androecium, and gynoecium.
• Calyx: The outermost floral whorl made of sepals, usually green and protective.
• Corolla: The whorl of petals, often brightly coloured or scented to attract pollinators.
• Androecium: The male reproductive whorl made of stamens, each usually consisting of a filament and anther.
• Gynoecium: The female reproductive whorl made of one or more carpels; each carpel may have stigma, style, and ovary.
• Ovary position: The ovary may be superior, as in hypogynous flowers; half-inferior, as in perigynous flowers; or inferior, as in epigynous flowers.
• Aestivation: The arrangement of sepals or petals in a floral bud, including valvate, twisted, imbricate, and vexillary types.
• Placentation: The arrangement of ovules within the ovary, including marginal, axile, parietal, free central, and basal types.
• Floral symmetry: The symmetry of a flower, which may be actinomorphic, zygomorphic, or asymmetric.
• Fruit: A mature or ripened ovary, usually formed after fertilisation, containing seeds.
• True fruit: A fruit that develops only from the ovary.
• False or accessory fruit: A fruit in which parts other than the ovary also contribute to fruit formation, such as the thalamus in apple.
• Seed: A mature ovule containing an embryo, reserve food, and a protective seed coat.
• Dicot seed: A seed usually having two cotyledons, such as pea or bean; it may be non-endospermic when food is stored mainly in cotyledons.
• Monocot seed: A seed having one cotyledon, called the scutellum; maize is a common example and usually retains endosperm.
• Floral formula: A symbolic representation of the important features of a flower, including symmetry, sex, floral whorls, ovary position, and fusion.
• Floral diagram: A graphical representation showing the number, arrangement, fusion, and relative positions of floral parts.

Easily Confused

• Tap root system vs fibrous root system: A tap root system has one prominent primary root and lateral roots, whereas a fibrous root system has a cluster of thin roots arising from the stem base.
• Tap roots vs adventitious roots: Tap roots develop from the radicle, whereas adventitious roots arise from stems or leaves.
• Root cap vs root hairs: The root cap protects the root tip, whereas root hairs arise in the zone of maturation and increase the surface area for absorption.
• Node vs internode: A node bears leaves, branches, or buds, whereas an internode is the stem portion between successive nodes.
• Stem tendrils vs leaf tendrils: Stem tendrils are stem modifications, as in grapes; tendrils are also included among leaf modifications when leaves become adapted for climbing.
• Reticulate vs parallel venation: Reticulate venation forms a network and is typical of dicots, whereas parallel venation consists of parallel veins and is typical of monocots.
• Simple vs compound leaf: A simple leaf has an undivided lamina, whereas a compound leaf has a lamina divided into distinct leaflets.
• Leaflet vs leaf: In a compound leaf, the axillary bud occurs at the base of the whole leaf, not at the bases of individual leaflets.
• Racemose vs cymose inflorescence: In racemose inflorescence the main axis continues to grow and flowers generally develop acropetally; in cymose inflorescence the main axis ends in a flower and flowers generally develop basipetally.
• Complete vs incomplete flower: A complete flower has calyx, corolla, androecium, and gynoecium; an incomplete flower lacks one or more of these whorls.
• Superior, half-inferior, and inferior ovary: A superior ovary characterises hypogynous flowers, a half-inferior ovary characterises perigynous flowers, and an inferior ovary characterises epigynous flowers.
• Actinomorphic vs zygomorphic flower: An actinomorphic flower has more than one plane of symmetry, whereas a zygomorphic flower has one plane of symmetry.
• True fruit vs false or accessory fruit: A true fruit develops only from the ovary, whereas a false or accessory fruit also includes other floral parts, such as the thalamus in apple.
• Dicot seed vs monocot seed: A dicot seed has two cotyledons, whereas a monocot seed has one cotyledon, the scutellum.
• Fruit formation after fertilisation vs parthenocarpy: Ordinary fruit formation generally follows fertilisation, whereas parthenocarpy produces fruit without fertilisation and can produce seedless fruits such as some varieties of banana.
• Floral formula vs floral diagram: A floral formula uses symbols to summarise floral features, whereas a floral diagram represents the number, arrangement, fusion, and relative positions of floral parts graphically.

What Gets Asked

• Identify a plant organ or modification from its example: questions may ask for the structure represented by ginger, potato, onion, grapes, Citrus, Bougainvillea, carrot, banyan, or mangroves. Marks are lost by confusing rhizomes, tubers, bulbs, stem tendrils, thorns, storage roots, prop roots, and pneumatophores.
• Compare monocot and dicot morphology: questions may require distinctions in root system and venation. The key slips are reversing tap roots and fibrous roots, or reticulate and parallel venation.
• Classify leaf arrangement and leaf type: examples include alternate phyllotaxy in China rose and mustard, opposite phyllotaxy in guava and Calotropis, and whorled phyllotaxy in Alstonia. Marks are lost by treating leaflets as separate leaves or by overlooking the axillary bud.
• Identify floral organisation: questions may test complete or incomplete flowers, bisexual or unisexual flowers, actinomorphic or zygomorphic symmetry, and hypogynous, perigynous, or epigynous ovary position. The common error is assigning ovary position without distinguishing superior, half-inferior, and inferior ovaries.
• Recognise aestivation and placentation from examples: China rose has twisted aestivation, pea has vexillary aestivation and marginal placentation, tomato and lemon have axile placentation, mustard has parietal placentation, Dianthus has free central placentation, and sunflower has basal placentation. Marks are lost by assigning an example to the wrong type.
• Explain fruit and seed formation: questions may ask how the ovary and ovules develop after fertilisation, or may test parthenocarpy, dicot seeds, and monocot seeds. The specific distinctions include the thalamus in the accessory fruit of apple, seedless fruits in some varieties of banana, two cotyledons in pea or bean, and the scutellum, coleoptile, and coleorhiza in maize.