Cirsium eatonii var. viperinum
Variety viperinum is apparently endemic to upper elevations of the Snake Range of White Pine County, Nevada. Heads of var. viperinum are similar in size to those of var. clokeyi. These taxa can be distinguished readily by the features in the key. Ranges of the two varieties are separated by about 340 km. Hybridization with Cirsium inamoenum is suspected based upon apparently intermediate specimens.