Sepal

A sepal (/ˈsɛp(ə)l/ or /ˈsiːp(ə)l/) is a part of the flower of angiosperms (flowering plants). Collectively the sepals are called the calyx, the outermost whorl of parts that form a flower. The word calyx adopted from the Latin calyx, not to be confused with calix, a cup or goblet. Calyx derived from the Greek καλυξ a bud, a calyx, a husk or wrapping, from Sanskrit kalika, a bud. Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom. After flowering, most plants have no more use for the calyx which withers or becomes vestigial, however, some plants retain a thorny calyx, either dried or live, as protection for the fruit or seeds. Examples include species of Acaena, some of the Solanaceae, and the water caltrop, Trapa natans. In some species the calyx not only persists after flowering, but instead of withering, begins to grow actively until it forms a bladder-like enclosure around the fruit. This is an effective protection against some kinds of birds and insects, for example in Hibiscus trionum and the Cape gooseberry.