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.
The terms used to describe aestivation are the same as those used to describe leaf vernation.
Classes of aestivation include:
- 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.
- ^ Hickey, M.; King, C. (2001). The Cambridge Illustrated Glossary of Botanical Terms. Cambridge: Cambridge University Press.