Plants usually unbranched or with age in some populations to 30 branches, most branches of largest clumps often immature, stems usually stiff and erect, smooth in immature plants to sparsely and coarsely needle-covered in adult plants. Roots ± diffuse, less than 1/4 of stem diam. Stems usually more than 1/2 above ground (sometimes deep-seated and flat-topped in winter, in cold climates and/or in immaturity), oblate, spheric, ovoid, obovoid, or cylindric with age, 2.5-20 × 3-11 cm; tubercles 8-25 × 3-8 mm, stiff or ± flaccid; areolar glands absent; parenchyma not mucilaginous (except possibly in far north); druses in pith and cortex present, some large, 0.7-1 mm diam., lenticular, usually conspicuous in old parts of stem; pith 1/5-2/3 of lesser stem diam.; medullary vascular system present. Spines 11-55 per areole; radial spines 10-40 per areole, weakly appressed or tightly appressed, pectinately arranged in subadults of some populations, either bright white, ashy white, pale tan, pale pinkish gray, or reddish brown (rarely stramineous), tips dark bright pinkish brown, reddish brown, dark brown, orange-brown, or pinkish orange on all or only largest spines (dark tips rarely absent), 7-22 × 0.08-0.6 mm; subcentral spines sometimes present in adaxial parts of clusters; central spines straight, snowy white, ashy white, reddish brown, sepia, purplish gray, pinkish gray, brownish red, pinkish brown, horn colored, pale tan, dark purplish brown, or stramineous, opaque or vitreous, fading, then blackening with age; outer central spines 3-14 per areole; inner central spines (0-)1(-4) per areole, appressed or strongly projecting, in "bird’s-foot" arrangement or radiating like spokes, longest spines 9-25 × 0.2-0.7 mm. Flowers slightly subapical, 20-57 × 25-67(-90?) mm; outer tepals conspicuously fringed; inner tepals 21-56 per flower, usually spreading, recurved, pale rose-pink to reddish pink or magenta, sometimes with darker midstripes, sometimes shading to white or pale greenish, proximally magenta, often darkest distally, 15-35 × 1.3-6 mm; outer filaments magenta or basally white (rarely entirely white or greenish white), seldom contrasting with inner tepals and, if so, then paler; anthers bright dark yellow (rarely orange-yellow); stigma lobes 5-13, erect or ascending, white to magenta, 2.5-5.5 mm. Fruits green, exposed portions slowly turning dull brownish red, ovoid to obovoid, 12-28 × 7-20 mm, juicy; floral remnant persistent. Seeds bright reddish brown, comma-shaped or nearly obovoid, (1-)1.3-2.4(-3) mm, pitted. 2n = 22.
"Stems solitary or in clumps, to 30 cm; tubercles elongate, 5–20 mm; areoles moderately woolly; central spines mostly 4, 1 pointing downward, 1–2 cm, red or basally white; radial spines 12–20, 1 cm, white; fls 4 cm, dark purplish-pink; fr green 1.2–2.5 cm; seeds brown, 1.5–2 mm; 2n=22. Dry, grassy plains; w. Minn. to Kans. and Okla., w. to Alta. and Ariz. May–Aug. (Mammillaria v.; Neomammillaria v.) Ours is var. vivipara."
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