Plant Morphology and Anatomy
External form
The exam tests root, stem and leaf modifications, inflorescence types, flower parts, aestivation, placentation and floral formulae. It also tests internal tissue arrangement in dicot and monocot organs.
Core rules
- Roots may be tap, fibrous or adventitious; storage roots include carrot and radish, respiratory roots are pneumatophores, and prop roots support banyan.
- Stems have nodes, internodes and buds; potato tuber, ginger rhizome, onion bulb and tendrils are stem modifications.
- Leaves have petiole, lamina and venation; phyllotaxy is alternate, opposite or whorled; leaves may be simple or compound.
- Racemose inflorescences have a main axis with lateral flowers; cymose inflorescences end in a flower.
- Aestivation includes valvate, twisted, imbricate and vexillary; placentation includes marginal, axile, parietal, free-central and basal.
- Anatomy: dicot stems have vascular bundles in a ring and open; monocot stems have scattered closed bundles; dicot leaves are dorsiventral; monocot leaves are isobilateral.
Worked example
Tomato has ovules attached to the central axis of a multilocular ovary, so its placentation is axile. Pea has ovules on a single marginal ridge, so it is marginal. Mustard has ovules on parietal partitions, so it is parietal. The reasoning depends on where ovules attach, not on fruit shape.
Traps
A bulb is a stem, not a root; potato is a stem tuber; sweet potato is a root tuber. Phylloclade and cladode are stems, not leaves. Do not confuse bracts with stipules. In floral formulae, K, C, A and G refer to calyx, corolla, androecium and gynoecium; fusion is shown by brackets.