Tepals are elements of the perianth, or outer part of a flower, which includes the petals or sepals. The term "tepal" is applied when all the segments of the perianth are of similar shape and color, or undifferentiated. 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.
Flowers of Magnolia × alba showing tepals in various development stages
See also 
- Augustin Pyramus de Candolle (1827). Organographie végétale, ou Description raisonnée des organes des plantes; pour servir de suite et de développement a la théorie élémentaire de la botanique, et d'introduction a la physiologie végétale et a la physiologie végétale et a la description des familles. Paris: Deterville. p. 503.
- 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.
Botany: A Brief Introduction To Plant Biology - 5th ed. Thomas L. Rost; T. Elliot Weier - Wiley & Sons 1979 ISBN 0-471-02114-8.
Plant Systematics - Jones; Samuel - McGraw-Hill 1979 ISBN 0-07-032795-5.