Sclerocactus parviflorusClover & Jotter: has stems from 4.5 to 45 cm tall, 3.5-14.5 cm in diameter. Radial spines 8-17 straight. Centrals 4-8 per areole, 1-5 hooked usually purple- black. Distribution: northern Arizona to Colorado, northern New Mexico and southeast Utah.
Sclerocactus parviflorus subs. havasupaiensis(Clover) Hochstätter: This subspecies shows similarities withSclerocactus polyancistruswhich occurs in California. Distribution: Havasupai Canyon (inside the Grand Canyon) in Arizona, USA.
Sclerocactus parviflorus subs. intermedius(Peebles) K.D.Heil & J.M.Porter: has long not hooked upper central spine flattened to 1-1.5(-2) mm broad and seeds at most 2.5 mm broad. Distribution: Utah, Arizona, Colorado, and New Mexico.
Stemsunbranched (occasionally 2-3-branched near base), green, ovoid to elongate-cylindric, 2.9-25(-35) × 2.8-12.5(-20) cm; ribs usually (11-)13(-15), well developed, tubercles evident on ribs.Spinesobscuring stems; radial spines 4-6 per areole, acicular, elliptic or rhombic in cross section, 19 × 1.3-2 mm; central spines 6-9 per areole, usually 8; abaxial central spine usually 1 per areole, porrect, straw colored to brown, highlighted with purple or red, terete or somewhat angled, hooked, (15-)30-46 × 1.5 mm; lateral central spines 5-8 per areole, similar to abaxial but slightly shorter and usually not hooked; adaxial central erect, white or straw colored, straight or curved, angled to flat, somewhat inconspicuous, triangular in cross section, 25-55 × 1-2 mm.Flowersnarrowly funnelform to campanulate, 2.5-3.5(-4) × 1.6-3.1(-3.6) cm; outer tepals with greenish to purple with brownish midstripes, pink, purple, or whitish margins, larger ones oblanceolate, 10-18 × 4-7.5 mm, margins membranous and crisped or minutely toothed, apex mucronate; inner tepals purple, sometimes suffused with brown, largest tepals oblanceolate, 15-22(-30) × 4-6 mm, margins irregularly toothed, apex mucronate; filaments white, tinged with pink to pink-purple; anthers yellow; ovary minutely papillate, appearing smooth.Fruitsirregularly dehiscent or dehiscent through basal abscission pore, green to tan, sometimes suffused with pink, 7-15 × 5-12 mm, dry; scales few, membranous, scarious-margined, minutely toothed or fringed.Seedsbrown or black, 1.2-2.5 × 1.9-3.5 mm; testa with rounded papillae.
Flowering late Apr-early Jun. Sandy, gravelly, or clay hills, mesas, and washes, desert grasslands, saltbush, sagebrush, and rabbitbrush flats, pinyon-juniper woodlands; 1500-2200 m; Colo., N.Mex.
Sclerocactus cloveraeis characterized by its very dense spines and small (relative toS. parviflorus) purple flowers. Phylogenetic analyses of chloroplast DNA sequences support a close relationship amongS. cloverae, S. whipplei,andS. parviflorus(J. M. Porter et al. 2000). Populations with all reproductive individuals maintaining juvenile morphology have been segregated asS. cloveraesubsp.brackiiK. D. Heil & J. M. Porter.