Labellum (botany)

Labellum (plural: labella) is the Latin diminutive of labrum, meaning lip.

It is not unusual for the other two petals of an orchid flower to look like the sepals, so that the labellum stands out as distinct.

Some have modified fleshy lumps on the upper surface generally referred to as the callus (plural: calli), with some being divided into multiple ridges or a central keel.

When the callus is flat and broad, it is sometimes called a plate, which can have fringed margins.

The callus can be highly modified with striking colors that may aid in pollinator deceit and mimicry.