Plants usually unbranched. Roots: upper portion of primary root somewhat thickened and succulent proximally, otherwise fibrous. Stems flat-topped or spheric, 4-8 × 4-8 cm, ± flaccid; tubercles 6-24 mm; axils appearing naked; cortex and pith mucilaginous; latex absent. Spines 9-31(-34) per areole, white, usually tipped brown; radial spines 8-30 per areole, in 1 series, glabrous (puberulent in first year flowering plants); lateral spines bristlelike, 7-11 mm, stiff, longest and thickest of spines; adaxial spines often darker; central spines 1-4(-7) per areole, porrect or strongly projecting, 1 or all hooked, (5-)12-14(-21) mm; subcentral spines 0. Flowers 2.5-3.5(-5.2) × 2.2-4.5(-7.5) cm; outer tepal margins conspicuously fringed; inner tepals rose-pink or magenta [white], margins often paler; stigma lobes yellow or pale green (rarely reddish). Fruits green or dull purple, spheric to ovoid or obovoid, (9-)13-20(-28) × (6-)7-1.9(-26) mm, juicy throughout; floral remnant persistent. Seeds black, 1.3-1.5 mm, pitted; testa hard, anticlinal cell walls straight (not undulate); interstices conspicuously narrower than pit diameters; pits bowl-shaped. 2n = 22.

Varieties 3 (2 in the flora): sw United States, Mexico.

SELECTED REFERENCE

Zimmerman, A. D. and D. A. Zimmerman. 1977. A revision of the United States taxa of the Mammillaria wrightii complex with remarks upon the northern Mexican populations. Cact. Succ. J. (Los Angeles) 49: 23-34, 51-62.