Phylogenetic Relationships of a North American Radiation of Clematis (Ranunculaceae)

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Clematis L. is one of many plant genera that contributes prominently to the species richness and endemism of the southeastern United States. Here we examined phylogenetic relationships among species in Clematis sect. Viorna, commonly known as leatherflowers, which are distributed primarily in the southeastern United States. We used data from restriction site-associated ddRADseq to reconstruct a best estimate phylogeny of this group. Our analyses revealed that the North American members of sect. Viorna form a well-supported clade, and several of the traditionally recognized infrasectional taxa were resolved as monophyletic. Although characters employed in classification including habit and inflorescence position appear highly labile within sect. Viorna, we find strong geographic structuring in the relationships, with a basal split between the Eastern and Western North American clades as well as clades of southeastern United States taxa largely confined to the Eastern or Western sides of the Mississippi River. The greatest undescribed taxonomic diversity remains in the southeastern United States, and the narrow endemism of many of these taxa underscores the pressing need for conservation efforts.