Aestivation in plants can define as the array of the perianth (a collective term for the sepals and petals) inside a floral bud. It is important to know the plant taxonomy, in which flowers of the different family show distinct aestivation. For instance, the sepals and petals of the Hibiscus flowers that belong to the Malvaceae family show valvate and twisted aestivation, respectively. In this context, we will discuss all the types of aestivation that the sepals or petals of a floral bud exhibit.
In the plants of the different family, valvate, twisted, imbricate, vexillary and quincuncial are the five common forms of aestivation , which generally exists. Therefore, aestivation is the property of sepals that shows its relation with the petals in floral bud or young flower. The term aestivation is more or less similar to the term vernation, which also describes the leaves organization interior to the vegetative bud.
Content: Aestivation in Plants
Definition of Aestivation
Aestivation is one of the floral characteristics, which elucidates the organization of calyx and corolla relative to each other, in a floral bud. Calyx and corolla can colloquially called as perianth. Thus, aestivation simply displays the array of the perianth, including sepals and petals. In a floral diagram, it is one of the property that is taken into consideration to show the relationship between the sepals and petals.
The calyx plus corolla constitutes the outermost whorl, i.e. perianth. In some plants, sepals and petals are found as auxiliary whorls, or we can say they are non-differentiated.
Example: Flowers of Polyanthus, Crinum, etc.
Sometimes sepals closely resemble the petals and are brightly coloured as in Gloriosa superba (Liliaceae ), Crinum asiaticum (Amaryllidaceae), etc. Flowers of Amaranthaceae family possess a membranous and persistent type of perianth.
The outermost whorl, i.e. perianth, will be termed as polyphyllous if the sepals and petals remain free, as in flowers of Gloriosa superba. But, if the sepals and petals are found fused as in the flowers of Polyanthes tuberosa, then the perianth will be termed as gamophyllous.
Types of Aestivation
The positional organization of sepals and petals are of following types :
It is open kind of aestivation, which includes flowers whose sepals and petals are only attached through the margins in a single whorl by leaving a free space within them. In simple words, the edges of calyx and corolla are very close within a floral whorl, but do not intersect each other.
Example: Mustard, Annona and Calotropis flower
It is also called contorted or convolute aestivation. It includes the flowers whose sepals or petals are organized in such a way, in which one edge overlaps the next edge inside. Thus they regularly overlap the neighbouring members on one side.
Example: Flowers of Hibiscus, ladyfinger and cotton.
In this kind of aestivation, the outermost whorl or perianth includes petals and sepals that overlap each other in a way that few petals are entirely inside and some are entirely outside. Thus, the overlapping of calyx or corolla in imbricate aestivation is non-specific, i.e. not occurs in a specific direction. Descending imbricate and ascending imbricate aestivation are the two common subtypes.
Example: Flowers of Gulmohar.
It is also known as papilionaceous or descending imbricate aestivation. In this type, the overlapping of petals starts from the posterior end towards the anterior side. It includes such flower, in which the odd posterior petal intersects the margin of two lateral petals. A pair of smallest anterior petals are overlapped by the two lateral petals or wings. Therefore, in such arrangement the largest or odd posterior petal is entirely outside, while the keel or anterior pair of petals are fully inside.
Example: Flowers of Tephrosia, Crotalaria and Dolichos.
It also refers as ascending imbricate aestivation and just contradicts the arrangement in descending imbricate aestivation. In this type, the overlapping of petals begins from the anterior end to the posterior one. In this type, the whorl of perianth is spirally arranged and not in a single whorl. The odd posterior petal is first intersected by the margins of two lateral petals, which in turn intersected by the anterior pair of petals. Thus, in such arrangement the odd posterior petal is entirely inside, the two lateral petals are partly external, and one of the two anterior petals is completely outside.
Example: Flowers in Cassia and Delonix.
Therefore, we can conclude that the aestivation is the array of perianth members, i.e. sepals and petals regarding each other. It is one of the factors, through which one can classify flowers, based on the type of aestivation.