Types of Aestivation

Types of Aestivation:

The Aestivation is of the given types:

1. Valvate Aestivation:

Petals or Sepals in a whorl merely meet by their edges without overlapping. Example:  Sepals of Hibiscus.

2. Twisted Aestivation:

In this mode of aestivation one margin of each and every sepal or petal overlaps the subsequent one, and the other margin is overlapped by a previous one. Here the over lapping is customary in one direction-clockwise or anticlockwise. Example: Petals of Hibiscus

3. Imbricate:

In this kind, one petal or sepal is internal or being overlapped on both the margins and one petal or sepal is external with both of its margins overlapping. Out of the remaining sepals or petals, one margin is overlapping and another margin is overlapped.

There are two forms of imbricate aestivation namely, descendingly imbricate and ascendingly imbricate.

a. Descendingly Imbricate or Vexillary Aestivation: 

In this form of aestivation the posterior petal overlaps one margin of the two lateral petals. Another margin of such two lateral petals overlaps the two anterior petals that are united.  Therefore the overlapping is in descending order and therefore the name. Example: Corolla of Fabaceae.

b. Ascendingly imbricate aestivation:

In this form the posterior odd petal is the innermost being over lapped by one margin of the two lateral petals. Another margin of the two lateral petals is overlapped by the two anterior petals. In this, the overlapping of petals starts from the anterior side proceeding towards the posterior side. This is just reverse of descendingly imbricate aestivation. Example: Petals of Caesalpiniaceae

4. Quincuncial:

This is a modification of imbricate aestivation in which the two petals are internal, two are external and the fifth one has one margin external and the other margin is internal. Example: Guava.

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 Figure: Different forms of Aestivation

 

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