A sepal (// or //) is a part of the flower of angiosperms (flowering plants). Collectively the sepals are called the calyx (plural calyces), 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.
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Magnoliophyta, also called angiosperms). The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs. Flowers may facilitate outcrossing (fusion of sperm and eggs from different individuals in a population) or allow selfing (fusion of sperm and egg from the same flower). Some flowers produce diaspores without fertilization (parthenocarpy). Flowers contain sporangia and are the site where gametophytes develop. Flowers give rise to fruit and seeds. Many flowers have evolved to be attractive to animals, so as to cause them to be vectors for the transfer of pollen.
In addition to facilitating the reproduction of flowering plants, flowers have long been admired and used by humans to beautify their environment, and also as objects of romance, ritual, religion, medicine and as a source of food.