Question

Describe vexillary aestivation with a suitable example.

Answer 1

Vexillary or descending imbricate aestivation is a feature of the Fabaceae family. Two lateral petals (wings) overlap two anterior petals (keel), which overlap the posterior largest petal (standard).

Complete answer:
Aestivation is the arrangement of floral parts inside a bud until it blooms into a flower. Aestivation refers to the arrangement of sepals or petals in a floral bud to other members of the same whorl.
There are several types of aestivation:
i) Twisted – an appendage is twisted if one of its margins overlaps the adjacent one in either a clockwise or anti-clockwise direction. Cotton is an example.
ii) Valvate – A whorl is valvate when the petals or sepals just touch the margin without overlapping. Calotropis is an example.
iii) Imbricate – An imbricate flower is one in which the petals or sepals overlap but not in any definite direction, as seen in Gulmohar.

Vexillary aestivation occurs when the largest petal overlaps the two lateral petals, which overlap the two smallest anterior peels. For example, Bean flower.
The arrangement in which the other smaller petals are covered by one large petal is known as vexillary aestivation. The larger petal is known as a vexillum, and the two curved petals that are laterally positioned are known as wings. The two innermost, boat-shaped petals are referred to as keels in this location. Polypetalous and papilionaceous are two examples.

Note: The quincuncial aestivation is a flower arrangement in which two petals or sepals are positioned internally, two petals or sepals are positioned externally, and the fifth part is located externally at the margin. Guava is an example of quincuncial aestivation.