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A lilium flower showing the petal-like tepals

Tepals are elements of the perianth, or outer part of a flower, which include the petals or sepals. The term tepal, derived from a combination of the words 'petal' and 'sepal,' 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 plants. Amborella, which is thought to have separated earliest in the evolution of flowering plants^[1], 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 first whorl of organs forms sepals, specialised for protection of the flower bud as it develops, while the second whorl forms petals, which attract pollinators.

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 of Hellebore.

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 with tepals

A Tulip showing the petal-like tepals

An Anemone flower showing the petaloid sepals

An Hellebore flower showing the petaloid sepals

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.