A tepal is a part of the outer part of a flower (the perianth) in which the petals and sepals are of similar shape and color, or undifferentiated, and therefore cannot be easily distinguished from one another. When different types of organs can be distinguished, they are referred to as sepals and petals. The term was first proposed by Augustin Pyramus de Candolle in 1827. De Candolle used the term perigonium (or perigone) for the tepals collectively; today this term is used as a synonym for "perianth".
Undifferentiated tepals are thought to be the ancestral condition in flowering plants. For example, Amborella, which is thought to have separated earliest in the evolution of flowering plants, has flowers with undifferentiated tepals. Distinct petals and sepals would therefore have arisen by differentiation, probably in response to animal pollination. In typical modern flowers, the outer or enclosing whorl of organs forms sepals, specialised for protection of the flower bud as it develops, while the inner whorl forms petals, which attract pollinators.
Undifferentiated tepals are common in monocotyledons. In tulips, for example, the first and second whorls both contain structures that look like petals. These are fused at the base to form one large, showy, six-parted structure. In lilies the organs in the first whorl are separate from the second, but all look similar, thus all the showy parts are often called tepals.
Usage of the term 'tepal' is inconsistent – some authors refer to 'sepals and petals' where others use the word 'tepals' in the same context.
Terms used in the description of tepals include pubescent (with dense fine, short, soft hairs, downy), puberulent (minutely pubescent, hairs barely visible to the naked eye) and puberulous (dense covering of very short soft hairs).
Flowers of Magnolia × alba showing tepals in various development stages
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- Augustin Pyramus de Candolle (1841). Vegetable organography; or, An analytical description of the organs of plants 2. translated by Boughton Kingdon. London: Houlston & Stoneman. p. 90.
- Stearn, William Thomas (2004). Botanical Latin (p/b ed.). David & Charles/Timber Press. ISBN 978-0-7153-1643-6. p. 39.
- Ronse De Craene, L. P. (2007). "Are Petals Sterile Stamens or Bracts? The Origin and Evolution of Petals in the Core Eudicots". Annals of Botany 100 (3): 621–630. doi:10.1093/aob/mcm076. PMC 2533615. PMID 17513305.
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