Aestivation and Perianth (With Diagram)!
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:
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:
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.
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.
This is the typical aestivation of the papilionaceous corolla. The posterior vexillum overlaps the two alae which again overlap the paired anterior carina.
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.
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.