Types of Corolla
Corolla is the second accessory whorl of a flower and the individual members of this whorl are called petals. Each petal consists of a narrow basal portion called the claw and an upper expanded portion called the limb. The petals may be polypetalous (free) or gamopetalous (united). The corolla may be actinomorphic (regular) or zygomorphic (irregular).
In a gamopetalous corolla the united basal portion is known as corolla tube and the upper free portions are known as the corolla lobes. Tube- like appendages develop from the corolla to store nectar. These are called the spurs.
The bright colour, the irregular shape and large sized corolla attract insects for pollination. The red, pink, blue and purple colour of the corolla is due to the presence of a pigment called anthocyanin. Corolla has two main functions, i e., to protect the inner whorls and attract the insects for pollination.
Types of corolla: There are various forms of corolla. Some of them are described below.
Polypetalous (free) and regular (actinomorphic):
- Cruciform: In this case, the corolla consists of four petals. The petals are free. The petals are arranged in the form of a cross and each petal has a distinct claw and a limb, for example, Raphanus (raddish), Brassica (mustard) etc.
- Caryophyllaceous: In this case, the corolla consists of five free petals with comparatively long claws. The claw and limb of each petal remain more or less perpendicular to each other, for example, Dianthus.
- Rosaceous: In this case, the claws of the petals are very short or absent and the limbs are comparatively larger and spreading. The number of petals may be five or more. The petals are free for example, Rosa.
Polypetalous and irregular (zygomorphic):
- Papilionaceous or Butterfly-like: In papilionaceous corolla, the corolla consists of five free petals. The outermost petal is the largest and is known as the standard or vexillum. The two lateral petals are the wings and the two innermost ones form a boat-shaped structure called the keel or carnia. The keel consists of the smallest petal. The general appearance of the Papilionaceous corolla is like a butterfly, for example, Pisum (pea), Dolichos (country bean), Clitoria (butterfly pea) etc.
Gamopetalous (united) and regular:
- Tubular: The corolla is said to be tubular when the petals become united to form a short cylindical tube-like structure with small lobes, as in the disc florets of Tagetes (marigold), Tridax, Helianthus (sunflower) etc.
- Campanulate or bell shaped: In Campanulate or bell shaped corolla, the petals are united and the corolla looks like a bell, for example, Cucurbita (gourd).
- Infudibuliform or funnel shaped: When the petals are united to form a tube below and gradually widened upwards, the corolla is called infundibuliform, for example, Datura, Ipomoea (water bind weed) etc.
- Rotate or wheel- shaped: In Rotate or wheel- shaped corolla, the corolla tube is comparatively short and the limbs spread at right angle to the corolla tube. The corolla looks like a wheel, for example, Solanum melongena (brinjal), Capsicum (chilli) etc.
- Hypocrateriform or salver shaped: In Hypocrateriform the corolla is very similar to that of rotate type but in this case, the corolla tube is longer and narrower and the corolla lobes are well spread, as in Vinca (periwinkle), Ixora (flame of the woods or jungle flame) etc.
- Uricolate. The corolla is said to be unricolate when the petals become united to form a tube, which is swollen at the middle and narrowed at both the ends as in Bryophyllum (sprout, leaf plant) etc.
Gamopetalous and irregular:
- Ligulate or strap shaped: When the corolla is tubular below forming a short narrow tube and plated above like a strap, it is called ligulate as in case of ray florets of Tridax (coat buttons or tridax daisy) Tagetes (marigold), Helianthus (sunflower)etc.
- Bilabiate or Bilipped: In bilabiate or billiped corolla, the corolla gives the appearance of two lips of the mouth. The lip of corolla is divided into upper portion and lower portion called the lips. The upper lip consists of two petals, while the lower lip consists of three petals. The mouth of the corolla remains wide open, for example, Ocimun (basil), Leucas, Hygrophila , Adhatoda (malabar nut) etc.
- Personate or Masked: The corolla is two-lipped in this case as in bilabiate but in personate corolla, the mouth is closed by a projection of the lower lip, known as the palate. The two lips are close to each other as in Antirrhinum (dog flower or snapdragon).