Mammillaria are generally small, delicate plants, usually forming clusters, with a wide variety of color, spination and flowers. Spines grow at the end of small tubercles rather than ribs - a characteristic shared with certain other species such as coryphantha and escobaria - and often include one of more longer central spines, which may be straight (pincushion cacti) or curved (fishhook cacti), surrounded by smaller radial spines. Flowers come not from the apex but lower down, in a ring around the upper part of the stem, and helps to distinguish them from similar species, as these tend to flower from the tip. Mexico has well over 100 species, the US only 14.


The other US mammillaria species, most uncommon, are:

Mammillaria macdougalii, MacDougal pincushion cactus, south Arizona between Tucson and Nogales (rare)
Mammillaria mainiae, counterclockwise fishhook cactus, Baboquivari Mountains in far south Arizona (rare)
Mammillaria prolifera, Texas pincushion cactus, along the Rio Grande from Del Rio to the Gulf of Mexico
Mammillaria sphaerica, longmamma pincushion cactus, far south Texas (rare)
Mammillaria thornberi, Thornber's pincushion cactus, south Arizona (Organ Pipe Cactus NM and Tohono O'Odham reservation)
Mammillaria viridiflora, green flowered pincushion cactus, south Arizona and far southwest New Mexico
Mammillaria wrightii, Wright's nipple cactus, southeast Arizona, southwest and central New Mexico, far west Texas