Mammillaria is one of the largest genera in the cactus family (Cactaceae), with currently 200 known species and varieties recognized. Most of the mammillarias are native to Mexico, while some come from the Southwestern United States, the Caribbean, Colombia, Guatemala, Honduras and Venezuela. The common name "pincushion cactus" refers to this genus and the closely related Escobaria.

The first species was described by Carl Linnaeus as Cactus mammillaris in 1753, deriving its name from the Latin mammilla, "nipple", referring to the tubercles that are among the distinctive features of the genus. Numerous species are commonly known as globe cactus, nipple cactus, birthday cake cactus, fishhook cactus or pincushion cactus (though such terms are also commonly used for related taxa, such as Escobaria or Ferocactus).

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