What is Calyx?

The calyx is the first part of a flower that develops and is close directly to the stem of the plant. Petals form inside the calyx along with the other parts of the flower. In many species of flowers, the calyx consists of leaf-like structures at the base of a flower that protect the flower during development of it. The leaf-like structures are individually referred to as sepals.

Types of calyx

Calyx can be classified on two basis, those are :

On the basis of size and shape :

i) Regular : The sepals of the calyx are of same size, e.g., chinarose.
ii) Irregular : The sepals are of different size, e.g., Cliteria.

On the basis of fusion :

i) Polysepalous : The sepals are free from each other, e.g., mustard.
ii) Gamosepalous : The sepals are united, they may be fully united to form a calyx tube as in Datura, or they may be partially united, with the upper part of the calyx lobe free, forming teeth-like structures, e.g.. Hibiscus.

Structural forms of calyx

The structural forms of calyx are studied under the two major types, viz. : regular gamosepalous and irregular gamosepalous.

Regular gamosepalous calyx :

The different forms of calyx under them are as follows :
i) Tubular: The calyx are united to form a tube-like-structure. e.g., Datura.
ii) Campanulate : The calyx lobes are united to form a bell-shaped structure, e.g., chinarose.

Irregular gamosepalous calyx :

In such case the calyx united, but the lobes are irregular.

Calyx of flower

i) Bilabiate : The calyx lobes form two distinct lip-like structures. The posterior upper lip consists of three sepals and the anterior lower lip consists of two sepals, e.g., Leonurus.

Modification of calyx

The sepals are modified to form various structures for serving various functions and they are as follows :
i) Pappus : The sepals tire modified to form a bunch of hairs or feather-like structures helping in seed dispersal, e.g. sunflower.
ii) Spinous : The sepals are modified to form pointed, spine-like stuructures. e.g. Water-chestnut (B. Paniphal).

iii) Scaly : The sepals are modified to scale like structure, e.g. sunflower [iv] Petaloid : The sepals are modified into large, coloured petal-like structures. e.g. Saraca indica (B. Ashoka), Mussanda.
iv) Hooded : One of the sepals are enlarged to form hood-like structure, e.g. Aconitum.
v) Spurred : The sepals are modified and prolonged into a tubular or beak-like structure, e.g. balsam.

Duration of calyx

The calyx normally persists till the formation of fruits. On the basis of duration of calyx in a flower, it can be classified in the following way :

i) Caducous or Fugacious :The sepals fall off even before the complete opening of flowers, e.g. Papaver (poppy).
ii) Deciduous : The sepals fall off along with petals just after fertilization, e.g. mustard.
iii) Persistent: The calyx is persistent and remain attached to the fruit. They are of two types.
a) Accrescent : The persistent calyx grows with the development of the fruit, e.g. brinjal, chalta.
b) Macrescent: The persistent calyx ceases to grow in a matured fruit e.g. tomato.