Question

Papilionaceous flower with large vexillum covering two wings and the wings covering the keel has corolla aestivation of
A. Descending imbricate
B.Ascending imbricate
C. Twisted
D. Valvate

Answer 1

Hint: The different modes of arrangement of petals or sepals in a flower bud with respect to the members of the same whorl is known as aestivation. It is of the following types- valvate, twisted or contorted, imbricate, and quincuncial.

Complete answer:
Papillionaceous flower consists of butterfly shaped irregular corolla with five petals. The posterior petal is largest and known as standard or vexillum. Two lateral petals are small and free called Wings or Alae, and are overlapped by the posterior standard petal. The two anterior petals are fused to form the innermost boat shaped structure covering the stamens and the carpels of the flower and is called Keel. It is overlapped by wings or alae. This arrangement is called descending imbricate and this type of arrangement is found in Pea and Lathyrus.
In ascending imbricate, the posterior petal is overlapped by two lateral petals which in turn are overlapped by two anterior petals, e.g. Cassia.
When one margin of a petal overlaps the adjacent petal lobe and the other margin is overlapped by adjacent petal, it is twisted arrangement. For example, Nerium and china rose.
In valvate arrangement, petals in a whorl are quite close to each other without overlapping, e.g. Mimosa and Acacia.
So, the correct answer is “Option A”.

Additional Information: In quincuncial arrangement, there are five petals, out of which two are external and two are internal. And the fifth petal has one margin external and one margin internal.

Note: Imbricate arrangement is an irregular type of overlapping of petals in the floral whorl and it is of two types- ascending imbricate and descending imbricate.