Structure and identification
For the nominate subspecies, the monograph describes flattened, grey-green stems, solitary or offsetting. Several central spines are longer and stronger than lateral ones, with one pointing forwards and the others upwards. Flowers range from pale pink to purple. The group described as subsp. santarosa has yellow flowers, a different stem colour and slightly sparser armature. The description retains this geographical variation. [Dicht and Lüthy 2005, p. 167–169]
Habitat and variation
The monograph documents the nominate subspecies in western Texas and neighbouring parts of Coahuila and Chihuahua, on limestone gravel and alluvial substrates at hill bases and on ridges. It associates the santarosa group with northern Coahuila. Its plants usually grow alone or in small clusters, among typical Chihuahuan Desert vegetation. [Dicht and Lüthy 2005, p. 167–169]