labellum

[ luh-bel-uh m ]

/ ləˈbɛl əm /

the petal of an orchid that differs more or less markedly from the other petals, often forming the most conspicuous part; the lip.

Origin of labellum

1820–30; < Latin, diminutive of labrum lip; for formation see castellum

la·bel·loid, adjective

This leads me to conclude that the labellum is always a compound organ.

More Letters of Charles Darwin Volume II |Charles Darwin
The ovaries in many cases were not twisted, so that the labellum was consequently uppermost.

Across Iceland |William Bisiker
This is important, as it explains all the astounding projections on the labellum of Oncidium, Phalaenopsis, etc.

More Letters of Charles Darwin Volume II |Charles Darwin
In a similar way the petals and labellum of Odontoglossum Uro-Skinneri have been found reduced to filamentous processes.

Vegetable Teratology |Maxwell T. Masters

The whole insect is of a bright pink colour, the large and oval abdomen looking like the labellum of an orchid.

Darwinism (1889) |Alfred Russel Wallace

labellum

/ (ləˈbɛləm) /

the part of the corolla of certain plants, esp orchids, that forms a distinct, often lobed, lip

a lobe at the tip of the proboscis of a fly

labelloid, adjective

C19: New Latin, diminutive of Latin labrum lip