thumb|upright=1.4|Diagram showing the parts of a mature flower. In this example the perianth is separated into a calyx (sepals) and corolla (petals)
A sepal ( or ) is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom. The term sepalum was coined by Noël Martin Joseph de Necker in 1790, and derived from the Greek σκεπη (skepi), a covering.
Collectively the sepals are called the calyx (plural calyces), the outermost whorl of parts that form a flower. The word calyx was adopted from the Latin calyx, not to be confused with calix, a cup or goblet. Calyx derived from the Greek κάλυξ (kalyx), a bud, a calyx, a husk or wrapping, (cf Sanskrit kalika, a bud) while calix derived from the Greek κυλιξ (kylix), a cup or goblet, and the words have been used interchangeably in botanical Latin.
After flowering, most plants have no more use for the calyx which withers or becomes vestigial. 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 (for example the Tomatillo, Physalis philadelphica), 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.
Morphologically, both sepals and petals are modified leaves. The calyx (the sepals) and the corolla (the petals) are the outer sterile whorls of the flower, which together form what is known as the perianth.
The term tepal is usually applied when the parts of the perianth are difficult to distinguish, e.g. the petals and sepals share the same color, or the petals are absent and the sepals are colorful. When the undifferentiated tepals resemble petals, they are referred to as "petaloid", as in petaloid monocots, orders of monocots with brightly coloured tepals. Since they include Liliales, an alternative name is lilioid monocots. Examples of plants in which the term tepal is appropriate include genera such as Aloe and Tulipa. In contrast, genera such as Rosa and Phaseolus have well-distinguished sepals and petals.
The number of sepals in a flower is its merosity. Flower merosity is indicative of a plant's classification. The merosity of a eudicot flower is typically four or five. The merosity of a monocot or palaeodicot flower is three, or a multiple of three.
The development and form of the sepals vary considerably among flowering plants. They may be free (polysepalous) or fused together (gamosepalous). Often, the sepals are much reduced, appearing somewhat awn-like, or as scales, teeth, or ridges. Most often such structures protrude until the fruit is mature and falls off.
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 (as in the Lythraceae family, and Fabaceae). In other flowers (e.g., Rosaceae, Myrtaceae) a hypanthium includes the bases of sepals, petals, and the attachment points of the stamens.
The Collaborative International Dictionary
Sepal \Se"pal\, n. [NL. sepalum, formed in imitation of NL. petalum, petal, to denote one of the divisions of the calyx: cf. F. s['e]pale.] (Bot.) A leaf or division of the calyx.
Note: When the calyx consists of but one part, it is said to be monosepalous; when of two parts, it is said to be disepalous; when of a variable and indefinite number of parts, it is said to be polysepalous; when of several parts united, it is properly called gamosepalous.
Douglas Harper's Etymology Dictionary
n. (context botany English) One of the component parts of the calyx, when this consists of separate (not fused) parts.
n. one of the green parts that form the calyx of a flower
Usage examples of "sepal".
In the scilla there is no corona, neither a tube, but the petal-like sepals or divisions of the perianth are entire, going to the base of the flower.
The petals were midnight-blue with a cream-colored frill, the sepals pure midnight-blue, elongate and twisting, the whole perianth dusted with gold flecks.
If the wicked ones meet with Berit in the place Sepal, he will not have the Flower-Gem with him to give to the wicked ones.
Each minute flower has four green petals and brownish seed organs, which cause the knob of flowers to have a rather grimy look, and a calyx which is very hard and stout, having two scales and four sepals.
The flowers have seven to ten sepals, are an inch across, and of a creamy white colour.
We start with the seed, from which we first imagine the cotyledons unfolding, letting this be followed by the gradual development of the entire green part of the plant, its stem and leaves, until the final leaves change into the sepals of the calyx.
But as soon as the petals wither, the sepals rise up and enclose the young capsule, forming a perfect roof over it as soon as the subpeduncle has bent itself downwards.
The sepals, which enclose the ovarium whilst it is young, present an additional adaptation by expanding widely when the seeds are ripe, so as not to interfere with their dispersal.
Side by side, two buds have been tossing jauntily in the breeze, often brought very near to each other, sometimes touching for a moment, with a secret thrill in their close-folded heart-leaves, it may be, but still the cool green sepals shutting tight over the burning secret within.
The limbs which had mimicked sepals struggled vainly for purchase upon the thorny green rings on which they had been mounted.
They all seemed unnaturally large and bright, and every one presented a great fan or bell of petals and sepals, surrounding a complex network of stamens and compound styles.
The flowerpeduncles, sepals, and petals, are studded with glandular hairs, like those on the leaves.
The flowerpeduncles, sepals and petals, bear glands in general appearance like those on the leaves.
It is familiar to almost every one, that in a flower the relative position of the sepals, petals, stamens, and pistils, as well as their intimate structure, are intelligible on the view that they consist of metamorphosed leaves, arranged in a spire.
Why should the sepals, petals, stamens, and pistils in any individual flower, though fitted for such widely different purposes, be all constructed on the same pattern?