Two novel tribes of Lamiaceae supported by phylogenomics and morphology

Plastome-based classifications recognize 12 subfamilies and 22 tribes within Lamiaceae. However, the deep phylogenetic relationships and tribal limits of Pogostemoneae sensu lato remain uncertain because nuclear phylogenomic investigations and assessments of cytonuclear discordance remain limited. We sampled all genera assigned to Pogostemoneae s.lat. and representatives of all recognized tribes of Lamiaceae. Transcriptome-based nuclear datasets and plastid datasets recover Lamioideae as monophyletic but Pogostemoneae s.lat. as non-monophyletic. Nuclear concatenation and coalescent analyses resolve three lineages: Pogostemoneae s.str. (six genera), Colebrookea and the Achyrospermum group, including Holocheila. We recircumscribe Pogostemoneae and describe Achyrospermeae and Colebrookeae as new tribes. At the tribal level, Pogostemoneae s.str. is distinguished by variable inflorescences and usually smooth, glossy nutlets; Achyrospermeae by frequent stellate tomentum, mostly dense spiciform inflorescences and usually dull, roughened or reticulate nutlets; and Colebrookeae by densely lanate-tomentose dioecious shrubs, strongly dimorphic flowers and accrescent fruiting calyces with elongate plumose teeth. Plastid trees usually recover the pogostemonoids as monophyletic, with conflict concentrated at the deepest backbone nodes. Conflict and gene flow analyses indicate pervasive incomplete lineage sorting, with localized introgression at specific nodes. Time-calibrated analyses date crown Lamioideae to the mid-Eocene (about 44 Ma), with major divergences near the Eocene-Oligocene transition. Speciation and net diversification rates increased towards the present across Lamioideae, without lineage-specific accelerations. These results provide a robust basis for revising the tribal classification in Lamioideae.