sepal, 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., the lily and the orchid) they are the same color as the petals and may be confused with them. In some groups of plants (e.g., the marsh marigold and the anemone) they are absent. The small green leaflike structures at the base of the flower head in the aster family are not true sepals but bracts; the sepals are modified into a circle of tiny white hairs on the ovary (the pappus; see aster). The sepals are sometimes fused into a tube around the base of the petals, as in the mint family.

A sepal (from Latin separatus "separate" + petalum "petal") is a part of the flower of angiosperms or flower plants. Sepals in a "typical" flower are green and lie under the more conspicuous petals. As a collective unit the sepals are called the calyx of a flower.

The calyx is part of the perianth of the flower. The perianth is composed of the sepals (collectively called the calyx) and the corolla (which is the outer part of the flower with the inner part of the perianth composed of the petals). The petals and sepals are usually differentiated into colorful petals and green sepals. But many flowers have colorful sepals and lack petals or the sepals and petals look similar and are often called tepals. The term tepal is usually applied when the petals and sepals are not differentiated and look similar or the petals are absent and the sepals are colorful. When the flower is in bud, the sepals enclose and protect the more delicate floral parts within. Morphologically they are modified leaves.

The number of sepals in a flower (called merosity) is indicative of the plant's classification: eudicots having typically four or five sepals and monocots and palaeodicots having three, or some multiple of three, sepals.

There exists considerable variation in form of the sepals among the flowering plants. Often the sepals are much reduced, appearing somewhat awn-like, or as scales, teeth, or ridges. Examples of flowers with much reduced perianths are found among the grasses. In some flowers, the sepals are fused towards the base, forming a calyx tube. This floral tube can include the petals and the attachment point of the stamens.

See also

Plant morphology