Plants unbranched or profusely branched (eastern populations), forming clumps to 30+ cm diam., spine-bearing areoles with short white wool not obscuring basal portion of spine. Roots ± diffuse or short taproots, sometimes adventitious from bases of branches. Stems deep-seated in substrate, becoming flat-topped and nearly subterranean in winter, oblate or spheric to obconic, 2-8 × (1-)1.8-7.5(-10) cm; tubercles 5-21 × 3-6+ mm, soft; areolar glands absent; parenchyma not mucilaginous; druses small and spheric; pith 1/5-1/3 of lesser stem diam.; medullary vascular system usually absent. Spines 6-21 per areole, bright white, pale gray, or pale tan, weathering to gray or yellowish brown, dark brownish orange to pale brown or pale grayish pink tips present on all or only the largest; radial spines 6-20 per areole, moderately to tightly appressed, 4-16 × 0.07-0.35 mm, excluding pubescence; outer central spines 0(-2) per areole, if 1, erect, if 2, ascending-spreading, 9-18 mm; inner central spines 0-1 per areole, porrect (rarely ascending or erect), straight, 8-20 × 0.2-0.4 mm. Flowers nearly apical, 18-50 × 15-50 mm; outer tepals fringed (rarely entire); inner tepals 13-25 per flower, pale greenish yellow to yellow-green with midstripes of green or rose-pink to pale brown; outer filaments brighter pink than inner tepals, pinkish with greenish white bases, or uniformly whitish; anthers bright yellow; stigma lobes 3-7, green or yellowish, 1-5 mm. Fruits orange-red to scarlet, sometimes proximally carmine or nearly magenta, spheric to ellipsoid, 6.5-10 × 5-9 mm, slightly succulent but not juicy, the funiculi papillate; floral remnant weakly persistent, often lost through weathering. Seeds black, nearly spheric to short pyriform, 1.4-2.2 mm., deeply pitted, outer cell walls concave. 2n = 22, 44.
Flowering Apr-Jun; fruiting Jan-Jun(-Jul). Plains, stony short-grass prairies, woodlands of ponderosa pine, pinyon, juniper, or Quercus gambelii, loamy places, often restricted to sedimentary rocks; Ariz., Colo., Kans., Mont., Nebr., N.Mex., N.Dak., Okla., S.Dak., Tex., Utah, Wyo.
Plants of Coryphantha missouriensis are localized, inconspicuous (except for their red fruits in spring), and difficult for non-specialists to distinguish from more common species. Reports of C. missouriensis from Idaho are based on misidentified specimens of Pediocactus simpsonii (in the broad sense). The record from southwestern New Mexico (L. D. Benson 1982) is based on immature Mammillaria heyderi var. bullingtoniana.
Stems solitary or in clumps, 5-10 cm; tubercles elongate, 12-15 mm; areoles very woolly; spines pubescent, at first yellowish, becoming dark gray; central spines 0-1(2), the radial ones 10-20, spreading, straight, 1-2 cm; fls 2.5 cm, yellow to yellowish-red; fr red, 1-2 cm; seeds black, 1 mm; 2n=44. Dry plains and hillsides, often among grasses; N.D. to Io., Mo., and Ark., w. to Mont. and Ariz. June, July. Ours is var. missouriensis. The var. caespitosa (Engelm.) L. D. Benson, with larger fls (ca 5 cm) and seeds (2.5 mm), may also be sought at our w. border.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.