'' flower showing the six
tepals: the outer three are sepals and the inner three are petals. Undifferentiated tepals are believed 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, and is specialised for protection of the flower bud as it develops, while the inner whorl forms petals, which attract
pollinators. Tepals formed by similar sepals and petals are common in
monocotyledons, particularly the "
lilioid monocots". 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 (the perianth). 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. Where sepals and petals can in principle be distinguished, usage of the term "tepal" is not always consistent – some authors will refer to "sepals and petals" where others use "tepals" in the same context. 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, for example, the sepals of
hellebores. When the undifferentiated tepals resemble petals, they are also referred to as "petaloid", as in
petaloid monocots, orders of monocots with brightly coloured tepals. Since they include
Liliales, an alternative name is lilioid monocots. == Properties and shape ==