Aestivation or estivation, refers to 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

Vernation

Vernation is the formation of new leaves or fronds. In plant anatomy, it is the arrangement of leaves in a bud....

: the arrangement of leaves within a vegetative bud.

Aestivation can be an important taxonomic diagnostic; for example Malvaceae

Malvaceae

Malvaceae, or the mallow family, is a family of flowering plants containing over 200 genera with close to 2,300 species. Judd & al. Well known members of this family include okra, jute and cacao...

 flower buds have valvate sepals, with the exception of the genera Fremontodendron and Chiranthodendron

Chiranthodendron

Chiranthodendron is a genus of flowering plants in the family Malvaceae, comprising a single species of tree, Chiranthodendron pentadactylon, is called the Devil's hand tree, monkey's hand tree, or Mexican hand tree, or some variant thereof - for the distinct shape of its flowers, which resemble an...

, which have sometimes been misplaced as a result.

The terms used to describe aestivation are the same as those used to describe leaf vernation.
Classes of aestivation include:

• cochleate
• contorted or twisted — every petal or sepal is outside its neighbour on one margin, and inside its neighbour on the other margin
• contortiplicate
• crumpled
• decussate
• imbricate — where one petal or sepal is outside all others, one is inside all others, and the others are outside on one margin and inside on the other
• induplicate
• open - petals or sepals do not overlap or even touch each other
• quincuncial
• reduplicate
• valvate — petals or sepals touch without overlapping