Aztekium ritteri (Boed.) Boed. Aztekium ritteri (Boed.) Boed. in Monatsschr. Deutsch. Kakteen-Ges. 1: 52. 1929 sec. Hunt 2016≡Echinocactus ritteri Boed. in Z. Sukkulentenk. 3: 305. 1928 syn. sec. Guzmán & al. 2003