Aestivation (botany)

Aestivation or estivation is the positional arrangement of the parts of a flower within a flower bud before it has opened. Aestivation is also sometimes referred to as praefoliation or prefoliation, but these terms may also mean vernation: the arrangement of leaves within a vegetative bud.

Aestivation can be an important taxonomic diagnostic; for example Malvaceae flower buds have valvate sepals, with the exception of the genera Fremontodendron and Chiranthodendron, which have sometimes been misplaced as a result.

Terminology
The terms used to describe aestivation are the same as those used to describe leaf vernation.

Classes of aestivation include:
 * crumpled
 * decussate
 * imbricate – overlapping
 * contorted or twisted – every petal or sepal is outside its neighbour on one margin, and inside its neighbour on the other margin.
 * cochleate – spirally twisted.
 * contortiplicate – contorted and also plicate.
 * quincuncial – with five parts, where two petals or sepals are outside all others, two are inside all others, and the fifth is outside on one margin and inside on the other.
 * induplicate – folded inwards.
 * open – petals or sepals do not overlap or even touch each other.
 * reduplicate – folded outwards.
 * valvate – margins of adjacent petals or sepals touch each other without overlapping.
 * vexillary – a special type of aestivation occurring in plants like pea; in this type of aestivation a large petal called standard encloses two smaller petals.