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Diagram showing the parts of a mature flower. In this example, the perianth is separated into a calyx (sepals) and corolla (petals) Mature flower diagram.svg
Diagram showing the parts of a mature flower. In this example, the perianth is separated into a calyx (sepals) and corolla (petals)
Tetramerous flower of Ludwigia octovalvis showing petals and sepals. Petal-sepal.jpg
Tetramerous flower of Ludwigia octovalvis showing petals and sepals.
After blooming, the sepals of Hibiscus sabdariffa expand into an edible accessory fruit Terengganu roselle.jpg
After blooming, the sepals of Hibiscus sabdariffa expand into an edible accessory fruit
In many Fabaceae flowers, a calyx tube surrounds the petals. Vicia February 2008-1.jpg
In many Fabaceae flowers, a calyx tube surrounds the petals.
The large calyx of the medlar fruit is the source of its vulgar nicknames. 20170919Crataegus germanica2.jpg
The large calyx of the medlar fruit is the source of its vulgar nicknames.

A sepal ( /ˈsɛpəl,ˈspəl/ ) [1] [2] [3] 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. [4]



The term sepalum was coined by Noël Martin Joseph de Necker in 1790, and derived from Ancient Greek σκέπη (sképē) 'covering'. [5] [6]

Collectively, the sepals are called the calyx (plural: calyces), [7] the outermost whorl of parts that form a flower. The word calyx was adopted from the Latin calyx , [8] not to be confused with calix 'cup, goblet'. [9] The Latin calyx is derived from Greek κάλυξ kalyx 'bud, calyx, husk, wrapping' (cf. Sanskrit kalika 'bud'), [10] while calix is derived from Greek κύλιξ kylix 'cup, goblet'; both words have been used interchangeably in botanical Latin. [11]


The term tepal is usually applied when the parts of the perianth 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 in petaloid monocots, orders of monocots with brightly colored 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. [ citation needed ]

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. [13] They may be free (polysepalous) or fused together (gamosepalous). [14] 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 family Lythraceae, [15] and Fabaceae). In other flowers (e.g., Rosaceae, Myrtaceae) a hypanthium includes the bases of sepals, petals, and the attachment points of the stamens.

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 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 . [17] In some plants, such as Aristolochia , the calyx is the primary whorl, forming a flower up to 20 inches (51 cm) wide, with one sepal growing to a length of 13 feet (4.0 m) Aristolochia grandiflora, the largest of all calyces. [18] [19]


Similarly to ordinary leaves, sepals are capable of performing photosynthesis. However, photosynthesis in sepals occurs at a slower rate than in ordinary leaves due to sepals having a lower stomatal 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 as Lodoicea and eggplant (Solanum melongena) 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 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 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. In other species, the calyx grows into an accessory fruit.

See also

Related Research Articles

<span class="mw-page-title-main">Petal</span> Part of most types of flower

Petals are modified leaves that surround the reproductive parts of flowers. They are often brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the corolla. Petals are usually accompanied by another set of modified leaves called sepals, that collectively form the calyx and lie just beneath the corolla. The calyx and the corolla together make up the perianth, the non-reproductive portion of a flower. When the petals and sepals of a flower are difficult to distinguish, they are collectively called tepals. Examples of plants in which the term tepal is appropriate include genera such as Aloe and Tulipa. Conversely, genera such as Rosa and Phaseolus have well-distinguished sepals and petals. When the undifferentiated tepals resemble petals, they are referred to as "petaloid", as in petaloid monocots, orders of monocots with brightly colored tepals. Since they include Liliales, an alternative name is lilioid monocots.

<span class="mw-page-title-main">Stamen</span> Male organ of a flower

The stamen is the pollen-producing reproductive organ of a flower. Collectively, the stamens form the androecium.

Calyx or calyce, from the Latin calix which itself comes from the Ancient Greek κάλυξ (kálux) meaning "husk" or "pod", may refer to:

<span class="mw-page-title-main">Lythraceae</span> Family of flowering plants

Lythraceae is a family of flowering plants, including 32 genera, with about 620 species of herbs, shrubs, and trees. The larger genera include Cuphea, Lagerstroemia (56), Nesaea (50), Rotala (45), and Lythrum (35). It also includes the members of the former families of the pomegranate and of the water caltrop. Lythraceae has a worldwide distribution, with most species in the tropics, but ranging into temperate climate regions as well.

<span class="mw-page-title-main">Tepal</span> One of the outer parts of a flower

A tepal is one of the outer parts of a flower. The term is used when these parts cannot easily be classified as either sepals or petals. This may be because the parts of the perianth are undifferentiated, as in Magnolia, or because, although it is possible to distinguish an outer whorl of sepals from an inner whorl of petals, the sepals and petals have similar appearance to one another. The term was first proposed by Augustin Pyramus de Candolle in 1827 and was constructed by analogy with the terms "petal" and "sepal".

<span class="mw-page-title-main">Floral symmetry</span> Shape of flowers

Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts.

<span class="mw-page-title-main">Perianth</span> Collective term for the sepals and petals, or either of them if one is absent

The perianth is the non-reproductive part of the flower, and structure that forms an envelope surrounding the sexual organs, consisting of the calyx (sepals) and the corolla (petals) or tepals when called a perigone. The term perianth is derived from Greek περί and άνθος, while perigonium is derived from περί and γόνος . In the mosses and liverworts (Marchantiophyta), the perianth is the sterile tubelike tissue that surrounds the female reproductive structure.

<span class="mw-page-title-main">ABC model of flower development</span> Model for genetics of flower development

The ABC model of flower development is a scientific model of the process by which flowering plants produce a pattern of gene expression in meristems that leads to the appearance of an organ oriented towards sexual reproduction, a flower. There are three physiological developments that must occur in order for this to take place: firstly, the plant must pass from sexual immaturity into a sexually mature state ; secondly, the transformation of the apical meristem's function from a vegetative meristem into a floral meristem or inflorescence; and finally the growth of the flower's individual organs. The latter phase has been modelled using the ABC model, which aims to describe the biological basis of the process from the perspective of molecular and developmental genetics.

<i>Bombax buonopozense</i> Species of tree

Bombax buonopozense, commonly known as the Gold Coast bombax or red-flowered silk cotton tree, is a tree in the mallow family. It is also known in the Dagbani language as Vabga.

This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology use a number of different terms to classify and identify plant organs and parts that can be observed using no more than a handheld magnifying lens. This page provides help in understanding the numerous other pages describing plants by their various taxa. The accompanying page—Plant morphology—provides an overview of the science of the external form of plants. There is also an alphabetical list: Glossary of botanical terms. In contrast, this page deals with botanical terms in a systematic manner, with some illustrations, and organized by plant anatomy and function in plant physiology.

This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary of leaf morphology. For other related terms, see Glossary of phytopathology, Glossary of lichen terms, and List of Latin and Greek words commonly used in systematic names.

A cyclic flower is a flower type formed out of a series of whorls; sets of identical organs attached around the axis at the same point. Most flowers consist of a single whorl of sepals termed a calyx; a single whorl of petals termed a corolla; one or more whorls of stamens ; and a single whorl of carpels termed the gynoecium. This is a cyclic arrangement.

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In botany, a whorl or verticil is a whorled arrangement of leaves, sepals, petals, stamens, or carpels that radiate from a single point and surround or wrap around the stem or stalk. A leaf whorl consists of at least three elements; a pair of opposite leaves is not called a whorl.

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Lilioid monocots is an informal name used for a grade of five monocot orders in which the majority of species have flowers with relatively large, coloured tepals. This characteristic is similar to that found in lilies ("lily-like"). Petaloid monocots refers to the flowers having tepals which all resemble petals (petaloid). The taxonomic terms Lilianae or Liliiflorae have also been applied to this assemblage at various times. From the early nineteenth century many of the species in this group of plants were put into a very broadly defined family, Liliaceae sensu lato or s.l.. These classification systems are still found in many books and other sources. Within the monocots the Liliaceae s.l. were distinguished from the Glumaceae.

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  1. From French sépale, from Neo-Latin sepalum, a blend of sep- from Greek skepē 'covering' and -alum from Neo-Latin petalum 'petal', influenced by French pétale 'petal'.
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