Genus Mammalaria has a presence in South America, North America, Mesoamerica and the Caribbean Basin. North American occurrences are limited to Mexico and the southwestern USA, with the center of genus diversity lying within Mexico. South American occurrences are restricted to the northern continent, particularly Venezuela and Colombia.
- C.Michael Hogan. 2011. Cactus. Topic ed. Arthur Dawson. Ed.-in-chief Cutler J.Cleveland. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC http://www.eoearth.org/article/Cactus?topic=49480