Aestivation

The mode of arrangement of plants (also sepals) in a flower bub with respect to members of the same whorl is known as aestivation.

• Valvate : When the petals of a whorl lie close to each other e.g., mustard.
• Twisted or contorted : When one margin of a petal of a whorl covers the margin of the adjacent petal and the other margin is covered over by the margin of adjacent petal. e.g. china rose.
• Imbricate :  When both margins of one of the petals are covered by the other and both margins of another one are external e.g., Cassia.

Imbricate aestivation is of two types :

1. Ascending imbricate : The posterior petal is innermost, i.e., its both margins are overlapped e.g., Caesalpinaceae such as Cassia , Bauhinia, etc.
2. Decending imbricate or vexillary : The anterior petal is innermost and the posterior petal is the largest and outermost e.g., pea, beans, etc.

Quincuncial :  It is a special type of imbricate aestivation in which 2 petals are external (both margins overlapping), 2 are internal (both margins overlapped) and in one petal one margin is overlapped and other overlapping e.g., Calyx of Cucurbita maxima, Corolla of Ranunculus.