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one of the four basic parts of a flower, next innermost organ from the sepal. The whorl of petals is known collectively as the corolla [Lat.,=little crown]. The number of petals is usually constant within groups (e.g.
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in flowers, the inner circle of small leaves (petals) of a double perianth. Petals forming the corolla may be free, separate (polypetalous corollas) or united (gamopetalous corollas, which have developed in the course of evolution from the polypetalous ones). The corolla is the most noticeable part of the flower, and in speaking of flowers one usually has in mind the corolla. The color of the corolla depends mainly on special pigments (anthocyanins and flavones) dissolved in the cell fluid. The biological role of the corolla is to make the flower more noticeable to insects that carry out cross-pollination of plants and to protect the stamens and the pistil. In the process of plant evolution the corolla developed from modified stamens that had lost their anthers or (more rarely) from top leaves. The endless variety of corollas in shape, detail of structure, color, and the like is a valuable aid in the taxonomy of plants.