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calyx(kā`lĭks): see sepalsepal,
a modified leaf, part of the outermost of the four groups of flower parts. The sepals of a flower are collectively called the calyx and act as a protective covering of the inner flower parts in the bud. Sepals are usually green, but in some flowers (e.g.
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the aggregate of usually green outer leaflets, or sepals, surrounding the corolla in flowers having a double perianth. The sepals are separate or fused.
The biological purpose of the calyx is to protect the flower’s internal organs and the developing fruit and to ensure supplementary feeding. In a few plants (Hydrangea, Erica, and some Ranunculaceae) the calyx is large and brightly colored and serves, instead of a corolla (which is either absent or underdeveloped), to attract insects. In some plants (Papaver) the calyx falls off when the flower opens; in others (Ranunculus) it falls off after the completion of flowering. In the majority of plants, however, the calyx remains after flowering and may even proliferate and participate in fruit formation. In Umbelliferae, Compositae, and some other plants the calyx is completely reduced or converted into hairs.