Abstract/Summary

Lamiaceae subtribe Plectranthinae, a palaeotropical group of just over 450 species with mainly zygomorphic flowers and stamens that are contiguous at the point of insertion at the base of the lower corolla lip, include the medicinally and horticulturally important genus Plectranthus. Plectranthus currently includes the formerly recognized Coleus and Solenostemon. A phylogenetic analysis of the group is presented based on rps16, trnL-F and trnS-G regions of the plastid genome. Plectranthus as currently recognized is paraphyletic; a clade containing the type of Coleus and including Solenostemon, Pycnostachys and Anisochilus is sister to the rest of the group. Three endemic and monotypic Madagascan genera, Dauphinea, Madlabium, Perrierastrum and the Madagascan Capitanopsis belong to a single clade and are recognized under Capitanopsis; the new combinations are made here. Plectranthus s.s. is sister to a clade comprising Thorncroftia and Tetradenia. Tetradenia, unlike any other members of Plectranthinae, has actinomorphic corollas and is usually dioecious. A group of other species previously recognized as Plectranthus form a clade separate from Plectranthus s.s. and is recognized as Equilabium gen. nov. Estimates of clade age suggest that the genera begin to diversify from the mid to late Miocene. Plectranthinae are found in dry woodlands, montane grasslands and evergreen forest margins. Shifts between habitats occur in most clades, although significantly fewer than if the changes were random. The distribution of the clades in the major habitats is examined. Migration in Plectranthinae was from Africa to Madagascar and Asia, and there is no evidence of migration back to Africa. The phylogenetic pattern of medicinal use in Plectranthinae is weak, and issues surrounding this are discussed.