- Tepal
Tepals are elements of the
perianth , or outer part of a flower, which include thepetal s orsepal s. The term tepal is usually used when all 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 petals and sepals.Undifferentiated tepals are thought to be the ancestral condition in
flowering plant s.Amborella , which is thought to have separated earliest in the evolution of flowering plants [ Louis P. Ronse De Craene "Are Petals Sterile Stamens or Bracts? The Origin and Evolution of Petals in the Core Eudicots" AOBPreview published on May 18, 2007, DOI 10.1093/aob/mcm076.] , 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 firstwhorl of organs forms sepals, specialised for protection of the flower bud as it develops, while the second whorl forms petals, which attractpollinator s.In some plants the flowers have no petals, and all the tepals are sepals modified to look like petals. These organs are described as
petaloid , e.g. the sepals ofHellebore .Undifferentiated tepals are common in
Monocotyledon s. Intulip s, 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.
Tulip showing thepetal -like tepals
Anemone flower showing the petaloidsepals 
Hellebore flower showing the petaloidsepals References
"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.
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