Equilabium Explained

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:

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