The arrangement of petals or sepals with respect to each other is known as aestivation. It is of following types:
VALVATE : Petals or sepals of a whorl meet by their edges do not overlap.
TWISTED: One margin of a petal overlaps the next and one overlapped by the preceding petal and so on. Twisting may be clockwise or anticlockwise.
IMBRICATE: In this one petal is completely internal one is external and in the remaining three petals one margin is internal one is external.
VAXILLARY: The posterior petal is largest & it overlaps the margins of two lateral petals and these lateral petals overlaps the two smallest anterior petals .This kind of aestivation is present in family Papilionaceae
QUINCUNCIAL: Two petals completely external two internal & the fifth has one margin external one internal.
