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Phylogeny of Citharexyleae

Citation

Frost, Laura et al. (2021), Phylogeny of Citharexyleae, Dryad, Dataset, https://doi.org/10.5061/dryad.31zcrjdk6

Abstract

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: Baillonia, Citharexylum—one of the largest genera in Verbenaceae—and Rehdera. A molecular phylogenetic approach was taken to resolve intergeneric relationships in Citharexyleae and infrageneric relationships in Citharexylum. 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 CitharexylumRehdera is resolved as sister to Citharexylum, and Baillonia nested within Citharexylum. Two species, C. oleinum and C. tetramerum, are not closely related to tribe Citharexyleae, but may be related to members of tribe Duranteae instead.  Seven clades within Citharexylum 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. Conclusions: A subgeneric classification for Citharexylum is proposed. Though suites of associated traits are found, character morphology has been labile throughout Citharexylum’s evolutionary history. Morphological diversity may be related to adaptation to differing mesic and xeric habitats.

Funding

National Science Foundation, Award: DEB 0542493

National Science Foundation, Award: DEB 0710026

National Science Foundation, Award: DEB 1020369

National Science Foundation, Award: DEB 1500919