Ortegocactus in Cact. Succ. J. (Los Angeles) 33: 39. 1961 sec. Vázquez-Sánchez & al. (2013)
Merging Ortegocactus in Mammillaria was proposed by Hunt & Taylor (1990) and Barthlott & Hunt (1993). The sole species O. macdougallii was first sampled by Butterworth & Wallace (2004) and found nested in Mammillaria, so the authors argued future transfer to Mammillaria may be justified, but must await further clarification of generic limits in this group. Vázquez-Sánchez & al. (2013) found O. macdougallii not nested in Mammillaria, but in a weakly supported polytomy in the mammilloid clade, suggesting maintaining it as a separate genus for the time being.