Phylogeny, classification, and character evolution of tribe Citharexyleae (Verbenaceae)

Premise of the study Tribe Citharexyleae comprises three genera: Baillonia, Citharexylum , and Rehdera . While there is good support for these genera as a clade, relationships between genera remain unresolved due to low sampling of the largest genus, Citharexylum . A molecular phylogenetic approach was taken to resolve intergeneric relationships in Citharexyleae and infrageneric relationships in Citharexylum . Methods Seven chloroplast regions, two nuclear ribosomal spacers, and six low-copy nuclear loci were analyzed for 64 species of Citharexyleae. Phylogenetic analyses were conducted using maximum likelihood, Bayesian inference, and Bayesian multi-species coalescent approaches. Habit, presence/absence of thorns, inflorescence architecture, flower color, fruit color, and geography were examined to identify diagnostic characters for clades within Citharexylum . Key results Intergeneric relationships resolved Rehdera as sister to Citharexylum and Baillonia nested within Citharexylum . Two species, C. oleinum and C. tetramerum , fell outside of Citharexyleae close to tribe Duranteae. There is strong support for seven clades within Citharexylum , each characterized by a unique combination of geography, fruit color/maturation, and inflorescence architecture. Conclusions Baillonia is included in Citharexylum; Rehdera is retained as a distinct genus. A subgeneric classification for Citharexylum is proposed.