The corolla refers to the collective group of all a flower’s petals, forming its most visually noticeable part with vibrant colors and intricate designs. Positioned within the sepals—typically green, leaf-like structures—the corolla and sepals together constitute the perianth, the flower’s outer protective and attractive whorls. This arrangement places the corolla as the second whorl, directly surrounding the flower’s reproductive organs.
The Function of the Corolla
The primary purpose of the corolla is to attract pollinators, such as insects, birds, and bats, facilitating the transfer of pollen for plant reproduction. The petals achieve this attraction through a combination of visual and olfactory cues. Their bright colors, derived from pigments like anthocyanins and carotenoids, act as clear signals to potential visitors.
The size and specific patterns on the petals also play a role in guiding pollinators towards the flower’s center. Many flowers produce scents from essential oils within their petals, further drawing in pollinators from a distance. Additionally, the corolla often contains nectaries, specialized glands that produce sweet, sugar-rich nectar, offering a reward for visiting animals.
Beyond attracting pollinators, the corolla provides physical safeguarding for the delicate reproductive structures of the flower, including the stamens and pistil. Before the flower fully opens, the petals enclose these parts, shielding them from environmental damage, adverse weather conditions, and potential herbivores. This protective role ensures the integrity of the reproductive organs until they are ready for pollination.
Variations in Corolla Forms
Corollas exhibit diverse structural arrangements, broadly categorized by whether their petals are separate or fused. Polypetalous corollas consist of distinct, individual petals that are not joined. Examples include roses and mustard plants.
Conversely, sympetalous corollas have petals that are at least partially fused, forming a single, unified structure. This fusion can result in a variety of shapes, from a simple tube to more complex forms. Datura and tomato flowers are common examples of plants displaying sympetalous corollas.
Corolla shapes vary significantly, each adapted for specific pollination strategies. Tubular corollas form an elongated, cylindrical tube with minimal spreading at the opening. Common in sunflower disc florets and plants like Datura, they often favor pollinators with long proboscises, such as hummingbirds or certain insects.
Campanulate corollas are bell-shaped, gradually widening from the base. Bellflowers and Physalis plants showcase this form, accommodating a range of pollinators that enter the open bell. Bilabiate corollas have two distinct “lips”—an upper and a lower—often providing a landing platform for insects. Snapdragons, Salvia, and Ocimum (holy basil) are examples, typically pollinated by bees interacting with these specialized lips.
Rotate corollas, also called wheel-shaped, feature a very short tube with a flat, circular limb where petals spread out at a right angle. Plants like tomatoes (Solanum species) and brinjal (eggplant) exhibit this form, allowing open access to reproductive parts for generalist pollinators. These diverse shapes highlight the intricate co-evolution between flowers and their pollinators.