Pantherophis emoryi

Burbrink (2002) used cytochrome b sequences to examine phylogenetic relationships among E. guttata populations (one specimen from each of 53 locations throughout most of the range). He found no support for recognition of the nominal subspecies intermontanus and meahllmorum as distinct taxa; these appear to be junior synonyms of E. guttata emoryi. Burbrink identified three partitions of E. guttata: an eastern partition (east of the Mississippi River) corresponding to E. guttata guttata, a western partition corresponding to E. guttata emoryi (including E. g. intermontanus and E. g. meahllmorum), and a central partition in western Louisiana and eastern Texas. The central partition, in pine and pine-hardwood habitat west of the Mississippi River, clustered closer to the eastern partition than to the western partition. Burbrink recognized the three partitions as species using evolutionary species criteria: (1) Elaphe guttata (red corn snake) (eastern partition ), (2) Elaphe emoryi (Great Plains rat snake) (western partition), and (3) Elaphe slowinskii (Slowinski's corn snake) (central partition). One specimen (Hidalgo County, Texas) of the central partition (based on cytochrome b characteristics) was located outside the presumed geographic area and habitat identified for other members of that partition. Crother et al. (2003) adopted these changes. Ernst and Ernst (2003) recognized E. emoryi and E. guttata as distinct species, but their manuscript evidently was completed before Burbrink's paper was published; they did not comment on E. slowinskii.

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.

The range extends from southwestern Illinois, Missouri, southern South Dakota, and southeastern Colorado southward to San Luis Potosi and Veracruz, and through most of Texas, with a disjunct population in eastern Utah and western Colorado (Conant and Collins 1991, Burbrink 2002).

This species is represented by a large number of occurrences (subpopulations).

No major threats are known. Locally, habitat destruction has reduced or eliminated some populations, but this species tolerates moderate levels of habitat alteration such as those associated with rural ranching activities.