Question

What do you mean by Aestivation? Explain types of aestivation.

Answer 1

This is an important phenomenon which is observed in the case of plants. This is an important feature that helps in the study of plant taxonomy, in which flowers of the distinct family show distinct aestivation. The term aestivation is more or less similar to the term vernation, which tells us about the organization of the leaves inside a vegetative bud. Calyx and corolla are together called perianth. They collectively constitute the outermost whorl. In a floral diagram, it’s one of the properties of a flower that is taken into consideration to show the relationship between the sepals and petals.

Complete answer:
Aestivation is the term used for the arrangement of calyx (sepals) and corolla (petals) in relation to one another in a flower.
Aestivation is of five different types :
1. Valvate – the type of aestivation in which sepals or petals are arranged in a whorl close together, and they do not overlap each other. Example: Calotropis.
2. Twisted – the type of arrangement in which one margin of the appendages overlaps the other one. One side of the petal is inside the other petal and the other side is outside another petal. This in and out arrangement of the petal is such that it looks twisted. Example: China Rose.
3. Imbricate – In this type of arrangement overlapping is there but not in a particular manner. One of the petals is completely inside and one of the petals is completely outside, but the rest of the petals are partially in and out. Example: Gulmohar
4. Vexillary – In this type of aestivation, five petals are differentiated into a large standard petal or vexillum that overlaps two lateral petals known as the wings which then overlaps the smallest anterior petal which is known as keel. Example: polypetalous.
5. Quincuncial- In this type of arrangement two petals are completely placed outside of the whorl and two are inside. The one that is left is present partially inside and partially outside. Example: Ranunculus.

Note:
There are two types of imbricate aestivation, which is the descendingly imbricate aestivation and ascendingly imbricate aestivation.
Descendingly imbricate aestivation: In this type, the posterior petal overlaps one margin of the two lateral petals. Hence, the overlapping is in descending order.
Ascendingly imbricate aestivation: In this type of aestivation, the posterior odd petal is innermost, being overlapped by one margin of the two lateral petals. Example - Cassia.