labellum

Labellum is a term in botany used to describe a floral structure that resembles a lip. The word comes from Latin labellum, a diminutive of labrum meaning lip, and is most often applied to the lower petal of a flower that is key to pollination in many species, especially the orchids.

In orchids, the labellum is typically a highly modified and conspicuous petal that differs from the other two petals and the sepals. It often serves as a landing platform for pollinators and can provide visual or tactile cues to guides pollinator movement toward the reproductive organs. The labellum may be flat or three-lobed, and it frequently bears features such as calli (ridges), glands, pigments, or patterns, and may include a nectar spur or a nectar-containing pouch.

A notable form is found in slipper orchids (Cypripedioideae), where the labellum is transformed into a pouch-like structure that temporarily traps pollinators and channels them toward openings where pollen attachment can occur. This specialization is a key example of how the labellum contributes to orchid pollination strategies.

Outside orchids, the term labellum can be used more generally to describe a conspicuous lower petal in some flowers, but its use is most prominent and defined within orchid morphology. The concept is part of broader studies of flower structure and pollination biology.