What is called Aestivation? Describe its types.

(N/A) The mode of arrangement of sepals or petals in a floral bud with respect to the other members of the same whorl is known as aestivation.
Its types are as follows:
$(i)$ Valvate: When sepals or petals in a whorl just touch one another at the margin,without overlapping,it is said to be valvate,e.g.,$Calotropis$.
$(ii)$ Twisted: If one margin of the appendage overlaps that of the next one and so on,it is called twisted,e.g.,China rose,Lady's finger,and Cotton.
$(iii)$ Imbricate: If the margins of sepals or petals overlap one another but not in any particular direction,the aestivation is called imbricate,e.g.,$Cassia$ and $Gulmohur$.
$(iv)$ Vexillary or Papilionaceous: In pea and bean flowers,there are five petals; the largest (standard) overlaps the two lateral petals (wings),which in turn overlap the two smallest anterior petals (keel). This type of aestivation is called vexillary or papilionaceous.