Corolla is composed of petals. Petals are generally brightly coloured to attract insects for pollination. Like calyx, corolla may be also free (gamopetalous) or united (polypetalous). The shape and colour of corolla vary in different plants. Corolla may be tubular, bell-shaped, funnel-shaped or wheel-shaped.
Aestivation: The mode of arrangement of sepals or petals in floral bud with respect to the other members of the same whorl is called aestivation. The main types of aestivation are valvate, twisted, imbricate and vexillary. In Valvate sepals or petals in a whorl just touch one another at the margin, without overlapping, as in Calotropis. In twisted, one margin of the appendage overlaps that of the next one and so on as in china rose, lady’s finger and cotton. In imbricate, the margins of sepals or petals overlap one another but not in any particular direction as in Cassia and gulmohur. In vexillary or papilionaceous, the largest (standard) overlaps the two lateral petals (wings) which in turn overlap the two smallest anterior petals (keel) as in pea and bean flowers