Genus of flowering plants
Equilabium is a genus of flowering plants in the family Lamiaceae. It was split off from the genus "Plectranthus" in 2018 as the result of a molecular phylogenetic study. Most species are native to Africa, with two found in the Indian subcontinent.
Description.
Species of "Equilabium" are herbaceous or soft-wooded shrubs, rarely woody shrubs. The herbaceous species may be annual or perennial. The leaves are opposite. The inflorescences are "thryses" – compound structures in which the flowers are arranged on secondary branches. Individual flowers have stalks (pedicels). The sepals form a two-lipped funnel shape, the upper lip having four lobes, the lower lip one lobe. The petals form a two-lipped tube, with an S-shaped basal portion. There are four stamens, whose filaments are not fused together. The style is divided into two parts (bifid). The nutlets are ovoid.
"Equilabium" and "Plectranthus" species are distinguished from "Coleus" by having the stem (pedicel) of the calyx attached symmetrically to the base of the calyx tube, rather than opposite the upper lip, and having the corolla lobes more or less equal in length. "Equilabium" species can be distinguished from "Plectranthus" by the truncated shape of the throat of the calyx and by the usually S-shaped tube of the corolla, which is parallel-sided at the base.
Taxonomy.
The genus "Equilabium" was first described in 2018 as the result of a molecular phylogenetic study. "Equilabium" was split off from the genus "Plectranthus", which was discovered not to be monophyletic. Only the names of the genus and the type species, "Equilabium laxiflorum", were formally published at the time. The names of 41 more species were published in 2019.
Phylogeny.
In 2019, Paton et al. published a summary cladogram for the subtribe Plectranthinae, based on an earlier 2018 study. The new genus "Equilabium" was established and "Coleus" revived. In the version below, the three genera accepted in these studies that were formerly included in a broad circumscription of "Plectranthus" are highlighted.
Species.
Paton et al. (2019) list 42 species:
References.
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