Question

'The flowers of many angiospermic plants which show sepals and petals, differ with respect to the arrangement of sepals and petals in respective whorls'. Explain.

Answer 1

Mode of the arrangement of sepals or petals in the floral bud, with respect to the members of the same whorls, is called aestivation. The main types of aestivation are valvate, imbricate, twisted and vexillary.

• Valvate: When sepals or petals just touch one another at the margin, without overlapping (eg. Calotropis).

• Twisted: One margin of sepals or petals overlap with that of next sepal or petal and so on (eg. China rose, ladies finger, cotton).

• Imbricate: Margins of sepals or petals overlap one another but not in any particular direction (eg. gulmohur, Casia).

• Vexillary/papilionaceous: Among five petals, the largest petal (standard) overlaps the two lateral petals (wings) which in turn overlap two smallest anterior petals (Keel petals). This is observed in pea and bean flowers.