Aestivation : The arrangement of sepals of petals with respect to one another in floral bud is called 'aestivation'.
Types of aestivation :
1. Valvate : The sepals or petals are arranged in a whorl which just touch one another at the margin, They do not overlap, e.g., Acacia, Calotropis, Solamint melongena.
2. Twisted : In this type of aestivation, one margin of a sepal or petal overlaps the next sepal or petal, and j next margin is overlapped by the proceeding one,resulting in a twisted appearance. Overlapping is always in the one direction only, e.g., China rose(petals), Cotton.
3. Imbricate : In this type of aestivation, the margins of sepals or petals overlap one another but not in any definite direction, e.g., Cassia fistuala (Amaltas- : Tejpata).
4. Vexillary : In this type of aestivation, the posterior petal is the largest and covers almost the two lateral petals, and the latter in their turn, nearly overlap the two anterior or smallest petals.