In a mature flower, theperianth consists of a calyx (sepals) and the corolla (petals) it supports.
Asepal (/ˈsɛpəl,ˈsiːpəl/)[1][2][3] is a part of theflower ofangiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for thepetals when in bloom.[4]
Tetramerous flower ofLudwigia octovalvis showing petals and sepalsAfter blooming, the sepals ofHibiscus sabdariffa expand into an edibleaccessory fruit.In many Fabaceae flowers, a calyx tube surrounds the petals.The large calyx of themedlar fruit is the source of its vulgar nicknames.
Collectively, the sepals are called thecalyx (plural: calyces),[7] the outermostwhorl of parts that form a flower. The wordcalyx was adopted from the Latincalyx,[8] not to be confused withcalix 'cup, goblet'.[9] The Latincalyx is derived from Greekκάλυξkalyx 'bud, calyx, husk, wrapping' (cf. Sanskritkalika 'bud'),[10] whilecalix is derived from Greekκύλιξkylix 'cup, goblet'; both words have been used interchangeably in botanical Latin.[11]
The termtepal is usually applied when the parts of theperianth are difficult to distinguish,[12] 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 inpetaloid monocots, orders of monocots with brightly colored tepals. Since they includeLiliales, an alternative name is lilioid monocots. Examples of plants in which the term tepal is appropriate include genera such asAloe andTulipa. In contrast, genera such asRosa andPhaseolus have well-distinguished sepals and petals.[citation needed]
The number of sepals in a flower is itsmerosity. Flower merosity is indicative of a plant's classification. The merosity of aeudicot flower is typically four or five. The merosity of amonocot orpalaeodicot flower is three, or a multiple of three.
The development and form of the sepals vary considerably amongflowering plants.[13] They may be free (polysepalous) or fused together (gamosepalous).[14] Often, the sepals are much reduced, appearing somewhatawn-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 thegrasses.
In some flowers, the sepals are fused towards the base, forming acalyx tube (as in the familyLythraceae,[15] andFabaceae). In other flowers (e.g., Rosaceae, Myrtaceae), ahypanthium includes the bases of sepals, petals, and the attachment points of thestamens.
Mechanical cues may be responsible for sepal growth and there is a strong evidence suggesting that microtubules are present and determine the tensile strength and direction of growth at a molecular level.[16]
Morphologically, both sepals and petals are modifiedleaves. The calyx (the sepals) and the corolla (the petals) are the outer sterile whorls of the flower, which together form theperianth.[17] In some plants, such asAristolochia, the calyx is the primary whorl, forming a flower up to 50 cm (20 in) wide, with one sepal growing to a slender ribbon with a length of up to 4 m (13 ft) inAristolochia grandiflora, the largest of all calyces.[18][19]
Similarly to ordinary leaves, sepals are capable of performingphotosynthesis. However, photosynthesis in sepals occurs at a slower rate than in ordinary leaves due to sepals having a lowerstomatal density which limits the spaces for gas exchange.[20]
After flowering, most plants have no more use for the calyx, which withers or becomes vestigial, although in a few plants such asLodoicea andSolanum melongena (aubergine, brinjal) the calyx grows along with the fruit, possibly to protect the attachment point. Some plants retain a thorny calyx, either dried or live, as protection for the fruit or seeds. Examples include species ofAcaena, some of theSolanaceae (for example thetomatilloPhysalis philadelphica), and thewater caltrop,Trapa natans. In some species, the calyx not only persists after flowering but instead of withering, begins to grow until it forms a bladder-like enclosure around the fruit. This is an effective protection against some kinds of birds and insects, for example inHibiscus trionum and inPhysalis species. In some other plants, the calyx grows into anaccessory fruit.
^From Frenchsépale, fromNeo-Latinsepalum, a blend ofsep- from Greekskepē 'covering' and-alum from Neo-Latinpetalum 'petal', influenced by Frenchpétale 'petal'.
^Davis, P.H.; Cullen, J. (1979).The identification of flowering plant families, including a key to those native and cultivated in north temperate regions. Cambridge: Cambridge University Press. p. 106.ISBN0-521-29359-6.
^Rohwer, Jens G. (2002).Tropical Plants of the World. New York: Sterling. p. 208.
