The problem with ratsnake taxonomy lies in what defines ratsnakes: a bunch of generalised colubrids, formerly lumped together into the genus Elaphe based on a lack of distinctive morphological characters. Morphologically distinctive sistergroups traditionally were outgrouped, which resulted in a highly paraphyletic Elaphe, an outcome considered as invalid by most taxonomist in general and cladists in particular.



For instance, American ratsnakes share a common ancestor with Kingsnakes and Pine/Bull/Gophersnakes. If we outgroup Lampropeltis and Pituophis from Elaphe, which we do, and include the American ratsnakes within Elaphe, which we no longer do, we get a paraphyletic Elaphe. However, if we consider Pantherophis as a sistergroup of Elaphe, which we do, we once again get nice and clean monophyletic taxonomical entities, well at least the American ones.



The resurrection of Pantherophis has been proposed by Utiger et al, based on an analysis of mitochondrial DNA and hemipenal morphometrics. It doesn't mean that Elaphe climacophora isn't similar morpholically to Pantherophis. It does mean, however, that E. climacophora and Pantherophis do not share a common ancester recent enough to belong to the same monophyletical genus.

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