The mode of arrangement of sepals/petals in a floral bud with respect to the other members of the same whorl is said to be aestivation. The following types of aestivation have been recognized.
When the members of a whorl are in contact with each other by margins, without overlapping or turning. e.g, Brassica, Calotropis.
When the members of a whorl rolled up in such a way that one margin of a member covers the margin of the other member and the other is covered by the one before it. e.g, Hibiscus, Abelmoschus, Gossypium, etc.
In imbricate aestivation, one member of the whorl is exterior, one interior, and the rest three having one margin exterior and the other interior. e.g, Cassia, Caesalpinia.
Of the five petals, the posterior one is the largest and nearly covers the two lateral petals, which in turn overlap s the two smallest anterior petals. This type of aestivation is a characteristic feature of papilionaceous corollas of the pea family.