Mammillaria rhodantha, the rainbow pincushion, is a plant in the cactus family and is one of 171 species in the genus Mammillaria which are characterized by having nipple-shaped tubercles or prominences on their surface. The rainbow pincushion is a small cactus usually ranging from 6 to 12 in (15–30 cm) in height. The cactus usually grows in small clumps or can be solitary. The stem is a short glabrous column that is covered with spikes. The entire plant body is covered with tubercles.