A lilium flower showing the tepals: the inner three are petals and the outer three are sepals.

Tepals are elements of the perianth, or outer part of a flower, which include the petals or sepals. The term perianth has two similar but separate meanings in botany In Flowering plants the perianth is the outer sterile whorls of a Flower (see A petal (from Ancient Greek petalon "leaf" "thin plate" regarded as a highly modified leaf is one member or part of the corolla A sepal (from Latin separatus "separate" + petalum "petal" is a part of the flower of Angiosperms or flower plants 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 plants. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group Amborella, which is thought to have separated earliest in the evolution of flowering plants^[1], has flowers with undifferentiated tepals. Amborella trichopoda is a rare vesselless understory Shrub or small Tree found only on the island of New Caledonia. 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. A pollinator is the biotic agent ( vector) that moves Pollen from the male Anthers of a Flower to the female stigma of a flower to accomplish

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. Commonly known as Hellebores, members of the genus Helleborus comprise approximately 20 species (ongoing fieldwork may see this figure change of Herbaceous

Undifferentiated tepals are common in Monocotyledons. Monocotyledons or monocots are one of two major groups of Flowering plants (angiosperms that are traditionally recognised the other being Dicotyledons In tulips, for example, the first and second whorls both contain structures that look like petals. Tulipa, commonly called tulip, is a Genus of about 150 species of bulbous Flowering plants in the family Liliaceae. 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

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.