Mammillaria difficilis Quehl in Monatsschr. Kakteenk. 18: 107. 1911 Mammillaria difficilis Quehl in Monatsschr. Kakteenk. 18: 107. 1911is basionym for Coryphantha difficilis (Quehl) Orcutt in Cactography: 3. 1926Taxon for this nameMammillaria difficilis Quehl