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.
Spring Snowflake (Leucojum vernum) and Summer Snowflake or Loddon Lily (Leucojum aestivum) are bulbous plants belonging to the Amaryllidaceae family, subfamily Amaryllidoideae. They are the only species currently classified in the genus Leucojum. The spelling Leucoium may also be found.
Leucojum is a compound of Greek leukos "white" and ion "violet".