Cheilos

Cheilos refers to the lips or labia of a flower. In botany, this term is specifically used to describe a type of corolla, the collective term for a flower's petals, that is divided into two distinct parts. These parts are often referred to as the "upper lip" and the "lower lip." The shape and arrangement of these lips can vary greatly among different species, and they often play a role in attracting pollinators by providing a landing platform or guiding them to the nectar.

The characteristic bilabiate or two-lipped structure is common in several plant families, including the Lamiaceae (mint family) and Scrophulariaceae (snapdragon family). The upper lip is typically formed from the posterior petals, while the lower lip is formed from the anterior petals. The fusion and modification of these petals create the distinct lip-like appearance. The specific morphology of the cheilos can be a key identifying feature for taxonomic purposes.

Pollination mechanisms are often closely linked to the structure of the cheilos. For example, in some flowers, the lower lip acts as a perch for insects, while the upper lip might protect the reproductive organs. The opening between the lips can also determine which pollinators can access the flower's nectar and pollen. The evolutionary development of the cheilos has been driven by the need to optimize pollination efficiency.