Molecular Phylogenetics of the Leucas Group (Lamioideae; Lamiaceae)

Abstract

The genus Leucas R.Br. includes 100 recognized species ranging in distribution from Africa through the Indian subcontinent to Queensland, Australia. Morphological cladistic studies have suggested that several other genera of Lamioideae – Acrotome, Isoleucas, Leonotis, and Otostegia (pro parte) – may be closely related to Leucas, or even nested within it. Here we use phylogenetic analysis of three plastid DNA loci, the trnL–F region, trnS–G spacer, and the rps16 intron and reach similar conclusions. Many of the morphological features used to maintain Leucas since 1810 are shared ancestral (symplesiomorphic) characters. The other genera (or subgeneric group in the case of Otostegia) are therefore defined by apomorphic states. This is particularly apparent in the case of Leonotis, with its highly specialized bird-pollinated flowers, derived within a paraphyletic and insect-pollinated Leucas. Some geographically isolated groups are monophyletic, including all Asian species of Leucas, a Socotran clade, and a large African lineage.