The genus-level taxonomy of the New World racers and whipsnakes (Coluber and Masticophis) has long been contentious regarding whether the two genera are mutually exclusive clades. This argument is based on morphological characters and largely single-locus analyses. Herein we examine the phylogenetic history of this group using multi-locus data in a coalescent framework, where paraphyly of Masticophis would result in support for the recognition of only a single genus (Coluber) for these species. We sample all currently recognized species and incorporate broad geographic sampling for the more widespread species groups to explore biogeographic patterns across North America. Our analyses suggest that Masticophis is monophyletic with respect to Coluber constrictor, albeit with low support. These results also demonstrate that there is undescribed cryptic diversity in this group, and we underscore additional avenues of study to further delimit unrecognized species in this clade. The biogeography of the island endemic, Masticophis anthonyi, is discussed with respect to what is known about other codistributed vertebrates. Lastly we provide an overview of the history of the arguments for or against the use of the generic name Masticophis and suggest its continued use.

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