Aestivation:

Aestivation may be defined as the mode of arrangement of sepals and petals in a floral bud with respect to the members of the same whorl (calyx or corolla).

The aestivation is of four main types

namely, valvate, twisted, imbricate and vexillary.

a) Valvate:

The aestivation is said to be valvate, when the margins of sepals or petals remain either in contact or lie close to each other but do not overlap,

e.g., Calotropis, calyx of Datura, etc.

 

b) Twisted or Contorted:

In this type one margin of each sepal or petal is directed inwards and is overlapped, while the other margin is directed outwards and overlaps the margin of adjacent one.

e.g.. Corolla of China rose, cotton, etc.

 

c) Imbricate:

In this type of aestivation one of the sepals or petals is internal and is overlapped at both the margins and one is external, that is, both of its margins overlap.

Rest of the sepals or petals have one inner or overlapped margin and the other outer or overlapping margin, e.g.. Cassia, Bauhinia, etc.

 

d) Vexillary:

In this type the corolla is butterfly shaped (papilionáceos) and consists of five petals.

Among these,

outermost and the largest is known as standard or vexillum,

two lateral petals, are known as wings and

two smaller, nearly fused petals forming a boat shaped structure are known as keel or carina.

The vexillum overlaps the two lateral wings.

The wings in their turn overlap the two other smaller innermost petals called keel.

e.g., pea, bean, etc.