Molecular phylogeny of tribe Stachydeae (Lamiaceae subfamily Lamioideae)

Although tribe Stachydeae (Lamiaceae) is considered monophyletic, relationships within the tribe are still poorly understood. The complexity of Stachydeae includes paraphyletic genera, considerable morphological plasticity, a range of ploidy levels, and presumably frequent natural hybridization. We performed parsimony and Bayesian phylogenetic analyses of nuclear (ribosomal ITS) and plastid (trnL intron, trnL-trnF spacer, rps16 intron) DNA sequence data from a taxonomically and geographically broad sampling of the tribe to identify major evolutionary lineages and to test taxonomic hypotheses within this largest of all lamioid tribes. We included 143 accessions corresponding to 121 species, representing both Old and New World species, and all 12 recognized genera of tribe Stachydeae. Both nuclear and plastid data corroborate monophyly of the tribe, with Melittis as sister to all remaining Stachydeae. For the latter well-supported clade, we suggest the phylogenetic name Eurystachys. Within Eurystachys, although monophyly is supported by both nuclear and plastid data for several named and unnamed groups, the majority of recognized taxa appear to be para- or polyphyletic. The taxon compositions of most subclades are congruent between the plastid and nuclear tree topologies, whereas their relative phylogenetic placements are often not. This level of plastid-nuclear incongruence suggests considerable impact of hybridization in the evolution of Stachydeae.