bilabiate [ bahy-LET-bee-it, -eyt ] adjective: having two lips
The first recorded use of the word bilabiate was in 1720, with the meaning still used today. In botany, the term is applied to flowers having long, narrow, tubular corollas, most often with a two-lobed upper lip and a three-lobed lower lip. A description on the University of Wisconsin’s website suggests that the flowers of Salvia guaranitica (blue anise sage), for example, “resemble an open parrot’s beak or snake’s mouth.”
Many of the bilabiate flowers are members of the Lamiaceae (formerly Labiatae, mint or sage family). With thousands of species comprising herbs, shrubs, and trees, the Lamiaceae have aromatic herbage, squared stems, and often whorl-like inflorescences (verticillasters); the leaves are usually opposite or whorled. Among those commonly seen in our gardens are the mints, monardas (bee balms), and salvias.
With their tubular form, bilabiate flowers attract hummingbirds, butterflies, and insect pollinators with long proboscises. Bilabiate flowers are lower in pollen concentration than some other flowers. Botanically, their form is specialized to protect the pollen from overharvesting by bees. According to one source, the feeding of a single bee offspring in its brood cell can require the pollen of between 7 and 1100 flowers.
Left to right: Monarda fistulosa, Monarda punctata, Physostegia virginiana, Salvia, Lobelia siphilitica.
But bees are an inventive species, and those with shorter tongues have devised ways to rob the nectar without going down long, narrow tubes. Robbing bees will chew or drill holes in the base of the tube and extract the nectar that way. This allows them to bypass the floral reproductive structures and obtain their reward without providing pollination services. The videos below show nectar robbers and a pollinator (ruby-throated hummingbird) of Monarda didyma ‘Jacob Cline’ (scarlet beebalm) as well as a variety of insects on Monarda fistulosa (wild bergamot), both native perennials with bilabiate flowers located at the Glencarlyn Library Community Garden in Arlington, Virginia.
References
Carr G. Lamiaceae. University of Hawaii Botany Department. (accessed August 27, 2021).
Mahr S. Blue Anise Sage. Salvia guaranitica. University of Wisconsin, Madison. (accessed August 27, 2021).
Westerkamp C. Classen-Bockhoff R. 2007. Bilabiate flowers: the ultimate response to bees? Annals of botany, 100(2), 361–374. doi: 10.1093/aob/mcm123.
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