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

Premise of the studyTribe 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. MethodsSeven 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 resultsIntergeneric 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. ConclusionsBaillonia is included in Citharexylum; Rehdera is retained as a distinct genus. A subgeneric classification for Citharexylum is proposed.