Structure and identification
For the nominate subspecies, the monograph describes hemispherical or spherical stems that produce offsets over time, with a densely woolly apex. Tubercles are closely spaced and lie against the stem. Pale lateral spines are arranged radially, with the upper ones more clustered. Dark central spines may be arched, but their number varies. The broad yellow perianth surrounds deep red staminal filaments. [Dicht and Lüthy 2005, pp. 150–152]
Habitat and variation
The authors associate the nominate subspecies with limestone gravel and alluvial soil at hill bases and on ridges in Puebla and Oaxaca. The group described as subsp. calipensis forms larger, more cylindrical stems and more strongly branched clusters. These differences retain the scope of the groups considered in the source. Former use of the name C. pycnacantha for some plants from Oaxaca was the subject of a detailed correction in the monograph. [Dicht and Lüthy 2005, pp. 150–152]
Related articles
Materials from the author's archive
The species also appears in Konrad Szychowski's private material archive. [Kaktologia 2009b, file p. 7] [Neciu b.d., file p. 1]