sepal

Sepals are the outermost floral organs of flowering plants. They are typically green, leaf-like structures that protect the flower in bud and enclose the developing reproductive parts. All the sepals together form the calyx, one of the two perianth whorls, the other being the petals of the corolla.

In most flowers, there are three to five sepals arranged in a whorl around the base of the flower. They can be free from one another (polysepalous) or fused at the base or along their length (gamosepalous). Sepals are often green and inconspicuous, but in some groups they are colored or petaloid and contribute to the flower’s appearance. In monocots, sepals and petals may be indistinguishable, and the floral organs are described as tepals.

Functions of sepals include protecting the flower bud before opening and, in many species, conducting photosynthesis that helps supply energy for flower development. When sepals resemble petals, they may assist in attracting pollinators. After pollination, the sepals may wither or persist; in some plants the calyx remains as a protective covering around the developing fruit or forms a calyx tube.

Various evolutionary patterns affect sepals: they may be reduced or highly reduced in some flowers, or transformed into petaloid structures in others. Thus, the presence, fusion, and coloration of sepals reflect broad diversity across angiosperms while remaining a defining feature of the calyx-an and perianth structure.