Solitary or branching cactus from south-central Mexico. Flowers are white, pale yellow or pale pink, with highlights on the midvein. This plant may or may not have central spines, and often has bristles or fuzz in the axils. Branching may occur at the base or dichotomously, by division of the growth center.

4 subspecies are recognized, based on distribution and spine count: Mammillaria (Mammillaria karwinskiana subsp. karwinskiana) (typically no central spine, ~6 radials); Biznaga de Beisel (Mammillaria karwinskiana subsp. beiselii) (1 central, 5-8 radials); Royal Cross (Mammillaria karwinskiana subsp. collinsii) (1 central, 7 radials); Biznaga de Nejapa (Mammillaria karwinskiana subsp. nejapensis) (no central, 3-5 radials).

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This plant is native to Mexico and Guatemala. It is characterized by white to yellow blooms, with 6 radial spines and no central spines. The spines are yellowish in color, and the plant takes a low, symmetric globular shape.

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