Corolla in plants is a second whorl that completes the perianth together with the layer of the calyx. It generally comprises several petals whose primary function is similar to the role of calyx that is to protect the flower reproductive structures. Corolla is also a sterile part of the flower. It can be tubular, funnel-shaped, wheel-shaped etc.
The size of the corolla is greater than that of the calyx. Petals are colourful and scented whose sole function is to attract the pollinating agents like bees, birds etc.
Content: Corolla in Plants
Meaning of Corolla
Corolla in plants can define as the group of petals that are prominently coloured, encircling the reproductive structures of a flower, i.e. stamen and carpel. Therefore, corolla individually refers as “Petals”. Corolla merely refers as the second whorl of a flower that is interior to the calyx. Like calyx, corolla can also be gamopetalous (fused) and polypetalous (free).
Features of Corolla
- Petals perform a significant role in protecting the essential floral parts in younger condition.
- Corolla is generally brightly coloured because of the presence of certain pigments like water-soluble anthocyanin, anthoxanthin, carotenoids etc.
- The petals are scented due to the presence of essential oil.
- The petals also contain tissues called “Nectaries” that produces sugar-rich nectar to attract insects.
- When the petals appear green or dull coloured, then they refer as “Sepaloids”. Example; Polyalthia, Annona etc.
- The petals are usually thin but can be thicker sometimes.
- The structure of petal comprises two components, namely claw and limb.
- Claw is a slender, basal part of a petal that appears stalk-like. Clawless bracts are sessile.
- A limb is an enlarged upper part of the petal.
- The shape and size of the petal can be regular or irregular.
- The symmetry of corolla can be radial or bilateral.
- Like leaf lamina, the edges of a petal can be entire, serrate, divided etc.
Types of Corolla
Like calyx, corolla can be free (polypetalous) or fused (gamopetalous). In polypetalous corolla, all the petals remain free in origin. In the gamopetalous corolla, the united and free portion refers as corolla tube, and corolla lobes, respectively and the junction of tube and lobe refers as “Throat”. The shape and size of the corolla in plants differ ranging between different species and can classify into regular or irregular form.
Cruciform: In this type, the orientation of petals appears as a cross that generally found in the members of the Cruciferae family, like mustard.
Rosaceous: It comprises of the clawless petals that only contains limbs expanding outwards, while the odd petal is anterior in position. It is common in the members of Rosaceous family, like a rose.
Caryophyllaceous: It comprises five free petals, where the claws and limbs are perpendicular to each other. It is common in the members of the Caryophyllaceae family, like dianthus.
Papilionaceous: It comprises five petals that resemble a butterfly. In papilionaceous corolla, the posterior petal or “Vexillum” is larger. Two inferior anterior petals or “Carine” are united, giving a boat-like appearance. There are other two lateral petals called or Alae, superimposing the carina. Example; Pea flower.
Tubular: In this type, the corolla tube is cylindrical, and the limbs are non-expanding. It is common in the members of the Compositae family. Example; Sunflower disc florets.
Campanulate: In this type, the corolla tube is rounded towards the base that gradually widens upwards, giving it a bell-like appearance. Example; Physalis.
Infundibuliform: Here, the petals are organized like an inverted funnel. Example; Datura.
Hypocrateriform: This kind of corolla appears as “Salver shaped” with a long and slender corolla tube and corolla limb at the right angle. Example; Vinca rosea.
Rotate: This kind of corolla resembles “wheel shape” with a shorter corolla tube and limbs at the right angle. Example; Solarium melongena.
Urceolate: In this type, the corolla tube is enlarged towards the middle and tapered towards both base and tip. Example; Kalanchoe pinnata.
Ligulate: This kind of corolla appears as “Strap shaped” which consists of five petals united to form a short tube at the base. The corolla tube splits on one side and becomes flattened like a strap. Example; Ray florets of marigold.
Bilabiate: It appears as two lip structure which consists of upper posterior and lowers anterior part. The upper posterior part comprises a union of two petals, while the unequal lower anterior part includes a coalition of three petals. Example; Leucas.
Personate: It is mask shaped corolla that somewhat resembles the shape of bilabiate flower. In personate corolla, both the limbs are held together due to which the mouth is closed. The projection of lower lip closing the mouth refers as “Palate”. Example; Snapdragon.
Functions of Corolla in plants
Corolla performs three functional tasks, like:
Pollination: The flower petals are brightly coloured, giving aromatic smell that grabs the attention of anyone. So, pollinating agents like bees, birds etc. help in the pollination of the flower.
Protection: The whorl of petals protect the reproductive structures of a flower, i.e. the male (stamen) and female (carpel) reproductive structures that participate in the fertilization of the flower to produce fruits.
Therefore, the corolla is a collective term for the group of petals that is the most attractive part of a flower because of their fluorescent colour and fragrance. It does not directly involve in the process of pollination, but indirectly it can captivate or repel the specific pollinators.