The arrangement of sepals or petals in floral bud with respect to the other members of the same whorl is called aestivation. Taxonomic point of view it is a important character.
1. Valvate: When sepals and petals just touch one another without overlapping. e.g., Calotropis, Annona etc.
2. Twisted or contorted: If one margin of the appendage overlaps that of the next one and so on in an particular direction, it is called twisted aestivation. e.g., China rose, lady's finger, cotton, Ixora etc.
3. Imbricate: In this case the the margins of the sepals and petals overlap one another but not in any particular direction is known as Imbricate aestivation. e.g., Cassia, Gulmohar etc.
4. Vexillary: It consists of largest petal called standard, which covers two lateral petals called wings. They in turn encloses two smaller petals called keel such aestivation is known as vexillary aestivation. e.g., Crotalaria, papilionaceous plants.
