Phylogeny of Citharexyleae

<p>As a family of Neotropical origin and primarily Neotropical distribution, the Verbenaceae are a good but understudied system with which to understand Neotropical evolution. Tribe Citharexyleae comprises three genera: <i>Baillonia</i>, <i>Citharexylum</i>—one of the largest genera in Verbenaceae—and <i>Rehdera</i>. A molecular phylogenetic approach was taken to resolve intergeneric relationships in Citharexyleae and infrageneric relationships in <i>Citharexylum</i>. The phylogeny is used to elucidate character evolution in a widespread, morphologically diverse Neotropical genus. Seven plastid 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 multi-species coalescent approaches. Habit, presence/absence of thorns, inflorescence architecture, flower color, fruit color, and geography were examined to identify diagnostic character states for clades within <i>Citharexylum</i>. <i>Rehdera</i> is resolved as sister to <i>Citharexylum,</i> and <i>Baillonia</i> nested within <i>Citharexylum</i>. Two species, <i>C. oleinum</i> and <i>C. tetramerum</i>, are not closely related to tribe Citharexyleae, but may be related to members of tribe Duranteae instead.  Seven clades within <i>Citharexylum </i>are inferred, each characterized by a combination of geography, fruit color/maturation, and inflorescence architecture. There is evidence of correlated evolution between habit, axillary inflorescences, and flower number per inflorescence. Shrubs with reduced inflorescences have evolved repeatedly. <i>Conclusions: </i>A subgeneric classification for <i>Citharexylum</i> is proposed. Though suites of associated traits are found, character morphology has been labile throughout <i>Citharexylum'</i>s evolutionary history. Morphological diversity may be related to adaptation to differing mesic and xeric habitats.</p>