A diagram showing some kinds of petal or sepal aestivation in flower buds. A: quincuncial; B: twisted, C: cochleate; D: contorted; E: valvate; F: open.

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.^[1]

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.