Crotalus viridis

Pook et al. (2000), Ashton and de Queiroz (2001), and Douglas et al. (2002) analyzed mtDNA sequence data and concluded that Crotalus viridis comprised at least two clades, C. viridis and C. oreganus, with C. cerberus being the sister taxon to populations of C. oreganus. The former two studies did not formally recognize C. cerberus as a species, although both suggested that it was distinct based on sequence differences and allopatry. The latter study did recognize C. cerberus as well as four other taxa. Although the studies relied on the same locus, Crother (2017) conservatively conclude that the congruence among all three studies might suggest the recognition of C. viridis, C. oreganus and C. cerberus. An unpublished study (Goldenberg 2013) suggests a unique lineage, that has not yet been named, occurs in the southern part of the nominate species' range, and that the subspecies as currently recognized do not correspond with the actual species-level divergences in the group (Crother 2017). Douglas et al. (2002) synonymized C. v. nuntius with C. v. viridis.

The traditional view of rattlesnake taxonomy that recognizes the two monophyletic sister genera Crotalus and Sistrurus (e.g. Brattstrom 1964) has recently been challenged. Stille (1987) and McCranie (1988) presented data that suggested Sistrurus is not monophyletic and rendered Crotalus paraphyletic. Parkinson (1999) found Sistrurus monophyletic but its position rendered Crotalus paraphyletic. Knight et al. (1993) used mtDNA to defend the traditional generic taxonomy, but in order to do so ignored the most parsimonious tree. The genus Crotalus is monophyletic when including the Mexican C. ravus (Murphy et al. 2002), and is supported as such in most recent phylogenies, as well as being the sister taxon to a monophyletic Sistrurus (e.g., Pyron et al. 2013) (Crother 2017). Davis et al. (2016) used mtDNA and morphometric analyses that resolved six species within the C. viridis complex, which Crother (2017) don't follow pending further analyses with nDNA.

Venom characteristics indicate hybridization between C. viridis and C. scutulatus in New Mexico (Glenn and Straight 1990).

As defined by Crother et al. (2003), following congruence of Pook et al. (2000), Ashton and de Queiroz (2001), and Douglas et al. (2002), this species encompasses only the ranges of subspecies viridis and nuntius of traditionally defined C. viridis. In other words, the range extends from southern Alberta and southern Saskatchewan to the northern fringe of northern central Mexico, west to Idaho, Wyoming, Colorado, and extreme eastern Arizona, east to the Dakotas, western Iowa, Nebraska, central Kansas, central Oklahoma, and western and central Texas (Stebbins 2003, Campbell and Lamar 2004). The ranges and relationships of Crotalus oreganus and Crotalus viridis in the Four Corners region and in northwestern Colorado need further clarification (Hammerson 1999; Brennan and Holycross, 2004, Herpetol. Rev. 35:190-191). Elevational range extends from about 100 meters near the Rio Grande (Campbell and Lamar 2004) to at least 2,895 meters (9,500 feet) in Colorado (Hammerson 1999).

This species is represented by a very large number of occurrences. On a range-wide scale, Campbell and Lamar (2004) mapped hundreds of collection sites (see also dot maps in Degenhardt et al. 1996 and Hammerson 1999).

No major threats are known. Locally, populations have been eliminated or depleted as a result of killing at dens and loss/degradation of habitat by residential, commercial, and agricultural development (Hammerson 1999).