Question

What is aestivation??

Explain its types in detail

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Answer 1

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Aestivation:

Aestivation may be defined as the mode of arrangements of sepals and petals in a floral bud with respect to the members of the same whorl is known as aestivation.

There are four types of aestivation :

1) Valvate aestivation:

The aestivation is said to be valvate, when the margins of sepals or petals remain either in contact or lie close to each other but do not overlap.

2) Imbricate:

In this type of aestivation one of the sepals or petals is internal and is overlapped at both the margins and one is external.

3) Twisted:

In this aestivation, one margin of each sepal or petal is directed inwards and is overlapped, while the other margins is directed outwards and overlap the margin of adjacent one.

4) Vexillary:

In this type, outermost and largest is known as standard, two lateral petals are known as wings and two smaller are known as keel.

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Answer 2

Aestivation:

Aestivation is the arrangement of either the sepals or the petals in a flower bud with relation to one another as vernation proper is the arrangement of young leaves in the vege­tative bud.

Aestivation is of considerable importance in the classification of plants. This may be of the following types :

(a) Floral Leaves in One Whorl

1. Valvate:

Floral leaves in a whorl may just touch one another at the margins without overlapping as seen in the family Anonaceae or the subfamily Mimoseae.

2. Contorted or twisted:

When overlapping is regular in one direction so that one margin overlaps the next member on one side while its other margin is overlapped by the one before, giving a twisted appearance to the bud.

This is seen in Malvaceae (china-rose, cotton, etc.) and Apocynaceae (Nerivm, Thevetia, etc.).

(b) Floral Leaves Not in One Whorl:

3. Imbricate:

When the margins overlap one another but not in any particular order as in the subfamily Caesalpinieae. In imbricate flowers the petals do not actually lie in a single whorl.

4. Quincuncial:

The floral leaves are not in a whorl but spirally arranged . Leaves 1 and 2 are external, 3 partly external, 4 and 5 internal. This is seen in guava (Psidium guyava of Myrtaceae), etc.

5. Vexillary:

This is the typical aestivation of the papilionaceous corolla. The pos­terior vexillum overlaps the two alae which again overlap the paired anterior carina.

Perianth:

In most monocotyledons the calyx and the corolla are not differentiated and the general accessory whorls form the perianth as seen in Polyanthes, Crinum, etc. The perianth is often brightly coloured or petaloid as in Gloriosa superba (Liliaceae ), Crinum asiaticum (Amaryllidaceae), etc. The perianth in some members of Amarantaceae is membranous and persistent. In Graminaceae the perianth is represented by two lodicules as seen in Festuca.

Flower of Festuca pratensis with lemma removed showing lodicules, feathery stigmas and versatile anther

If the perianth members are free from one another as in Gloriosa superba , the perianth is termed polyphyllous. When the perianth members are united as in Poly­anthes tuberosa , the perianth is gamophyllous.

Polyphyllous petaloid periath in gloriosa superba flower

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