Structure and identification
For the nominate subspecies, the monograph describes spherical or short-columnar stems, broad at the base, with tubercles narrowing to an almost round cross-section. The main central spine ends in a distinct hook. Lower lateral spines spread radially, while upper ones gather in layers. Flowers are whitish yellow, with a very pale throat. The group described as subsp. geoffreyi has smaller, flattened stems and more pronounced clustering. [Dicht and Lüthy 2005, p. 154–157]
Habitat and variation
The authors associate the nominate subspecies with sandy-clay alluvial plains with a high gypsum content in Nuevo León and San Luis Potosí. For the geoffreyi group, they document deeper red grassland soils at higher elevation, surrounded by pine forests. These differences concern specific geographical groups and are retained in the habitat descriptions. [Dicht and Lüthy 2005, p. 154–157]