Difference Between Sepals & Petals
Botanists classify flowers as complete or incomplete. Complete flowers have four parts: pistils, stamens, petals and sepals. The first two are the sex organs -- the male stamen and the female pistil. The sepals encase the leaflike petals.
Collectively, sepals are referred to as the calyx of the flower, from the Greek "kalyx," meaning "seed pod, husk, outer covering." The sepals, or calyx, protect the petals from the elements while the flower is still in bud form.
In some flowers -- sunflowers, for example -- sepals are green, making them easy to distinguish from the brightly coloured petals. The sepals on these plants resemble a kind of transition from stalk to flower -- green-hued like the former, but shaped more like the latter.
In flowers such as lilies, amaryllises and orchids, the petals and sepals look very similar, and are called tepals. Distinguish the sepals from the petals by looking closely at these flowers and observing two layers -- an inner and an outer whorl. The external layer is the sepals. These types of flowers have three petals and three sepals.
Incomplete flowers lack one or more of the four parts complete flowers have. Clematis and hydrangeas are two examples of incomplete flowers -- look at the petal-like parts and you'll see only one layer or whorl, which means the plant only has sepals -- the petals are missing.
Some flowers, such as camellias and roses, appear to have not only sepals and petals, but additional inner layers of more petals. This is because one or both sex organs of the plant have been transformed into petals. These are called petaloid pistils or petaloid stamens. Identify the flower parts by position, and move outwards to find the sepals -- they are usually green on double flowers, and are located outside and beneath the petals.