John M. Coulter: Preliminary Revision of the North American Species of Echinocactus, Cereus, and Opuntia. In: Contributions from the United States National Herbarium. Band 3, Nummer 7, 1896, S. 423–424 (online).
doi.org
Richard Crook, Roy Mottram: Opuntia index, Part 7. P–Q. In: Bradleya. Band 19, 2001, S. 115 (doi:10.25223/brad.n19.2001.a11).
