[Coryphantha calochlora Boed., more]
Plants unbranched (western) to freely branched and ± forming mats (eastern), tuberculate with numerous, fine spines. Roots diffuse or short taproots; branches root adventitiously. Stems deep-seated, aerial portion hemispheric or ± flat-topped, less than 11 × (4-)5.2-7 cm; tubercles 7-10(-13-) × 10 mm, firm; areolar glands seasonally conspicuous; parenchyma not mucilaginous; pith 1/2 of lesser stem diam.; medullary vascular system conspicuous. Spines 13-21 per areole; uppermost radial spines white, contrasting with others, at least on old plants, sometimes forming conspicuous white tufts, others white to tan or dark brown; radial spines 13-20 per areole, 13-23 × 0.15-0.17 mm; central spines 0-1 per areole, porrect, straight or slightly curved downward, longest spines 11-16 mm. Flowers apical or nearly so, 45-50 mm diam.; outer tepals entire; inner tepals ca. 30 per flower, pale yellow, ca. 30 mm; outer filaments white or pale yellow; anthers orange-yellow; stigma lobes 5-8, white or cream, (2.5-)5-8 mm. Fruits gray-green or bright green (paler proximally), obovoid, spheric, or ellipsoid, 18-23 × 8-10 mm; floral remnant strongly persistent. Seeds orange, drying to reddish brown, spheric to comma-shaped, 1.1-1.7 mm, finely and weakly raised-reticulate. Flowering summer (Aug-Sep). Tamaulipan thorn scrub, eastern edge of Chihuahuan Desert, limestone outcrops, nearby alluvium; of conservation concern; 100-150 m; Tex.; Mexico (Coahuila, Nuevo León, Tamaulipas). Coryphantha nickelsiae often has ribbonlike uppermost radial spines.