Pantherophis spiloides

Burbrink et al. (2000) and Burbrink (2001) examined genetic and morphological variation in Elaphe obsoleta as traditionally defined and determined that the nominal subspecies do not represent evolutionary lineages and should no longer be recognized. Further, these authors identified three clades within E. obsoleta, corresponding to populations (1) west of the Mississippi River (western clade), (2) east of the Mississippi River and west of the Appalachian Mountains and Apalachicola River (central clade), and (3) east of the Appalachians and the Apalachicola River (eastern clade). Burbrink (2000) recognized the three clades as distinct species: E. obsoleta (western clade), E. spiloides (central clade), and E. alleghaniensis (eastern clade). In mapping the distribution of the species, Burbrink indicated a very large area of "taxonomic uncertainty" extending from New England to northern Georgia. In this region the distribution of E. alleghaniensis was deemed "somewhat questionable with regard to hybridization with members of Elapahe spiloides." Although Burbrink concluded that the molecular data show that E. alleghaniensis and E. spiloides represent independently evolving units with separate evolutionary histories and thus should be recognized as different species under the evolutionary species concept, contact zones were not critically examined, so the nature and dimensions of clade boundaries, and the precise distributions of alleghaniensis and spiloides along the length of the Appalachians, remain uncertain.

Elaphe bairdi, confirmed as a valid species by Burbrink (2001), was included in Elaphe obsoleta by some authors in older literature.

Utiger et al. (2002) examined mtDNA variation in New World and Old World "Elaphe" and determined that North American rat snakes currently included in the genus Elaphe form a monophyletic limeage that is distinct from Old World snakes that also have been regarded as Elaphe. They resurrected the genus Pantherophis for the rat snakes north of Mexico, including the following species: Pantherophis obsoletus (and P. alleghaniensis and P. spiloides, if one recognizes those taxa as species), P. guttatus, P. emoryi, P. vulpinus, P. gloydi, and P. bairdi. Based on mtDNA and nuclear DNA data, Burbrink and Lawson (2007) determined that New World Elaphe are not closely related to Old World Elaphe. While further splitting of Pantherophis has been proposed (Collins and Taggart 2008), the use of Pantherophis has helped stabilize the classification of New World ratsnakes. Thus, Crother (2017) refrain from further division of the genus.

Large range in eastern North America; large area of occupancy; presumed large population size; trend uncertain: information is needed on population impact of snake fungal disease. Better information is needed on distribution relative to Pantherophis alleghaniensis.

This species occurs west of the Apalachicola River and the Appalachian Mountains and east of the Mississippi River, from western New York, southern Ontario, southern Michigan, and southwestern Wisconsin to southeastern Louisiana, southern Mississippi, southern Alabama, and western Florida; eastern edge of range along the Appalachian Mountains is poorly defined, and a large area of taxonomic uncertainty potentially involving hybridization with P. alleghaniensis extends from eastern New York and New England to northern Georgia (Burbrink 2001).

The number of distinct occurrences has not been determined using consistent criteria, but this species is represented by a very large number of collection sites and locations (as defined by IUCN).

Intensive agricultural development and urbanization have caused localized declines, and collectors probably have depleted some easily accessible populations, but in most areas this snake is not threatened by these factors. This species is likely vulnerable to snake fungal disease; the scope, severity, and population impact of this disease are uncertain but potentially significant.