Mammillaria sempervivi var. caput-medusae (Otto ex Pfeiff.) Backeb., Cactaceae 5: 3160. 1961 Mammillaria sempervivi var. caput-medusae (Otto ex Pfeiff.) Backeb., Cactaceae 5: 3160. 1961is new combination for Mammillaria caput-medusae Otto ex Pfeiff., Enum. Diagn. Cact.: 22. 1837Taxon for this nameMammillaria sempervivi var. caput-medusae (Otto ex Pfeiff.) Backeb.