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Aestivation/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.

References※

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