Corolla, is a flower in all the petals of the general term, is located in the calyx above or inside, arranged in a round or more rounds, more with bright colors, before the flower opens to protect the internal structure of the flower, after the flower opens to attract insects to pollinate by the beautiful color.

The corolla is relatively thinner than the sepals, and its structure is similar to that of the segments but lacks chloroplasts. The bright colors of the petals mainly come from the colored bodies in the cells and the anthocyanin pigments (flavonoids) in the vesicles. When containing chromosomes, petals are often yellow, orange, or orange-red; while anthocyanin-containing petals are often red, blue, or purple (mainly determined by the pH of the cellular fluid in the vesicle). The combination of the two makes the flowers of angiosperms colorful, and the petals are white when both are absent. The epidermal cells of the petals often contain volatile oils, which give the flowers a variety of special aromas. There are often nectar glands at the base of the petals, which can secrete nectar to attract insects.

Petals are in many cases isomorphic, such as buttercups, begonias, hickory flowers, petals of the same shape and size, called neat flowers. But in some taxa, the petals often occur obvious differentiation, such as legumes peas, astragalus, etc. petals are differentiated into the form of different sizes of flag petals, wing petals and keel petals, orchids within the round of the petals of a piece of specialization for the large and beautiful labellum, etc., this type of flower is known as the untidy flower.

Some flowers have long or short tubular projections extending from the petals, called spurs, such as the violet groundsel, columbine, and crocus.

Some plants have petals that are differentiated into a gable and a claw, i.e., the upper part of the petal is enlarged to form the gable, and the base of the petal is narrowed to form the claw, e.g., the flowers of Dianthus and Oleander.

Sometimes the petals are specialized into special forms of nectar leaves and lose their original form, e.g. the petals of Aconite.

In the flowers of some plants, additional petal-like or corolla-like accessory structures called corona exist between the petals and the stamens, e.g., the flowers of Malvaceae, Narcissus.