Morphology of Flowering Plants

The root is the underground part of the plant that anchors it, absorbs water and minerals, and often stores food. It originates from the radicle of the embryo.

Types:

• Tap root system — primary root develops from radicle; common in dicots (e.g., mustard, carrot).
• Fibrous root system — primary root short-lived; replaced by adventitious roots; common in monocots (e.g., wheat, grass).

Root modifications (and their functions):

• Storage roots — carrot (fusiform), radish (napiform), sweet potato (tuberous, adventitious).
• Prop roots — arise from stem, provide extra support; e.g., banyan tree.
• Stilt roots — arise from basal nodes of stem; e.g., maize, sugarcane.
• Pneumatophores — arise from roots in mangrove plants; grow upward for gaseous exchange; e.g., Rhizophora.
• Respiratory roots — arise from stem nodes in mangroves.

Stem bears leaves, branches, flowers, and fruits at nodes. Internodes separate the nodes. Stem grows towards light (positively phototropic).

Stem modifications:

• Underground — rhizome (ginger), corm (colocasia), tuber (potato), bulb (onion).
• Subaerial — runner (grass), stolon (strawberry), offset (water hyacinth), sucker (chrysanthemum).
• Aerial — tendrils (cucumber), thorns (Bougainvillea), phylloclade (Opuntia), bulbil (Agave).

Leaf is the primary site of photosynthesis; consists of leaf base, petiole, and lamina.

• Venation: Reticulate (dicots — peepal), Parallel (monocots — grass).
• Phyllotaxy: Alternate (China rose), Opposite (Calotropis), Whorled (Nerium).
• Leaf modifications: Tendrils (Pisum — leaflets), Spines (Opuntia), Pitcher (Nepenthes), Bladder (Utricularia).

Inflorescence — the arrangement of flowers on the floral axis:

• Racemose — main axis continues to grow; younger flowers at top; e.g., mustard, radish.
• Cymose — main axis ends in a flower; growth limited; e.g., Solanum.

Parts of a flower: Calyx (sepals) → Corolla (petals) → Androecium (stamens) → Gynoecium (pistil/carpel).

Aestivation — arrangement of petals/sepals in the bud:

• Valvate — edges touch, no overlap (e.g., Calotropis).
• Twisted — one margin overlaps next (e.g., China rose, cotton).
• Imbricate — overlapping, no definite direction (e.g., Cassia, Gulmohar).
• Vexillary — largest petal (vexillum) overlaps two lateral wings, which overlap two smallest keels (e.g., pea — Fabaceae).

Placentation — arrangement of ovules in the ovary:

• Marginal (pea), Axile (tomato, lemon), Parietal (mustard, Argemone), Free central (Dianthus, Primrose), Basal (sunflower).

Fruit develops from the ovary wall (pericarp) after fertilisation. A true fruit develops only from the ovary; false fruits include receptacle or other floral parts (e.g., apple, strawberry).

Seed develops from the ovule:

• Dicot seed (e.g., gram) — seed coat (testa + tegmen), two cotyledons, embryo axis (plumule + radicle).
• Monocot seed (e.g., maize) — seed coat fused with fruit wall; one cotyledon (scutellum); plumule covered by coleoptile; radicle by coleorhiza; endosperm present and large.