sepal
sepal, any of the outer parts of a flower that primarily serve to enclose and protect the unopened flower bud. The sepals on a flower are collectively referred to as the calyx. They may be either green or leaflike or composed of petal-like tissue. In contrast to the more short-lived petals and stamens, sepals are commonly persistent and evident when the fruit matures (e.g., persimmon, Cape gooseberry, rose, and eggplant).
In a complete flower the sepals are one of four organs attached to the floral stalk by a receptacle; from outward inward, the other three organs are the petals, male stamens, and female carpels. These floral organs are often united or fused, and the basic floral pattern typically consists of alternating whorls of organs positioned concentrically. Thus, in a complete five-merous flower there would be a whorl of five sepals, followed by an alternating whorl of five petals, followed by an alternating set of five stamens, and a central carpel. The number of sepals is usually the same as the number of petals. The sepals and petals—which together form the perianth—are accessory parts or sterile appendages; though they protect the flower buds and sometimes attract pollinators, they are not directly involved with sexual reproduction.
- Related Topics:
- calyx
Sepals can be separate from each other (aposepalous, or polysepalous) or fused (synsepalous), forming a tube with terminal lobes or teeth. Sepals may be brightly colored and function as petals in flowers that are missing true petals—for example, Clematis and Bougainvillea. When the color and appearance of sepals and petals are similar, as in the tulip tree (Liriodendron tulipifera) and Easter lily (Lilium longiflorum), the perianth is said to be composed of tepals. Petaloid sepals can be distinguished from tepals by the orientation of the stamens. When true petals are absent, the first group of stamens are on the same radii as the petaloid sepals; in flowers with tepals, the stamens are positioned normally on alternating radii in the next floral whorl.