Hypsiglena chlorophaea

Taxonomy of Hypsiglena has received some critical review since Tanner's revision of the genus in 1944. Dixon (1965) and Dixon and Dean (1986) studied a morphological contact zone between northern and southern taxa at the Sonora–Sinaloa border in Mexico, finding that it comprised a narrow zone of hybridization with some taxa existing in sympatry. Hardy and McDiarmid (1969) examined specimens across the range of this presumptive contact and elsewhere in western Mexico and concluded that no morphological characters existed to separate torquata and ochrorhyncha, except maybe nuchal patterns, which they decided (p. 170) was "a case of pattern dimorphism in a single, otherwise uniform, species." Grismer et al. (1994) dismissed the recognition of subspecies in Baja California, stating, without evidence, that the subspecies intergrade widely. Mulcahy (2008) conducted a comprehensive phylogeographic study of Hypsiglena based on an mtDNA analysis of >150 individuals. Mulcahy (2008) recognized six species in what was considered H. torquata, five of which are consistent with previously described lineages (e.g. subspecies), while one represents a unique lineage that remains to be described. Mulcahy (2008) also recommended maintaining the subspecies designations for several of the widespread, polymorphic species, which may represent incipient species. The nominal species H. torquata is now restricted to Mexico, three described forms occur in the USA, and the undescribed form is endemic to the Cochise Filter Barrier area of southeastern Arizona and associated New Mexico (Crother 2017).

Range extends from south-central British Columbia south through Washington, Oregon, southern Idaho, eastern California, Nevada, Utah, western Colorado, northern, western, and much of southernwestern Arizona, northeastern Baja California, and northwestern mainland Mexico (Mulcahy 2008).

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

No major threats have been identified. In many areas the rocky habitat tends to be unsuitable for incompatible human uses.