Corolla is the second whorl of flower and made up of petals. In dicotyledons the number of petals is usually five (variation from 2-10) and in monocotyledons three. The petals may be polypetalous or gamopetalous. The inferior and superior position of petals and their duration is like that of sepals. Petals are usually variously coloured. Sometimes they are green e.g., in Artobotrys and polyalthea.
Forms of corolla
I. Symmetrical and Polypetalous :
1. Cruciform : It consist of 4 petals arranged crosswise, each petal is clawed e.g., Mustard.
2. Caryophyllaceous : It consists of 5 petals, each with a comparatively long claw and the limbs of petals are placed at right angles to the claw, e.g., Dianthus.
3. Rosaceous : It consists of 5 petals. Petals are with short claws or none. The limb spreads regularly outwards e.g., Rose.
4. Campanulate or Bell shaped : bell e.g., Physalis
II. Symmetrical and gamopetalous :
1. Tubular : In this case the corolla is tubular or cylindrical e.g., Central florets of Sunflower .
2. Infundibuliform or Funnel shaped : When the corolla is like a funnel e.g. , Datura.
3. Rotate or Wheel shaped : When the tube of the corolla is narrow and short and the limbs are at right angles to the tube e.g., Brinjal.
4. Salver shaped or Hypocrateriform : When in a rotate type the corolla tube is comparatively long e.g., Ixora
III. Monosymmetrical and polpetalous :
1. Papilionaceous : It is composed of five petals out of which one posterior is largest and is known as standard or vexillum., the two lateral ones, partially covered by standard are known as wings or alae, and the two innermost anterior smaller are united to form a boat shaped structure keel or carina. e.g., pea, gram (members of Papilionatae).
IV. Monosymmetrical and Gamopetalous :
1. Bilabiate (Two lipped) : The whole corolla is divided into two lips — the upper lip and lower lip, with the mouth gaping wide open, e.g., Ocimum, Adhatoda.
2. Ligulate or Strap-shaped : When the upper part of corolla is flattened like a strap with the lower part forming a short tube e.g., outer florets of Sunflower.
3. Personate or Masked : In this case also the corolla is bilabiate but the lips are so near to each other as to close the mouth of the corolla e.g., Antirrhinum.