Cact. Succ. J. (Los Angeles) 32: 193. 1960.
Plants branched or unbranched. Stems globular to short cylindric, 0.7–5.5 × 1–3 cm; areoles circular, villous. Spines smooth, relatively hard, all radial, mostly 18–26 per areole, spreading, recurved, or somewhat pectinate, reddish tan, pink, or white, 1–1.5 mm, canescent. Flowers 1–3.5 × 1–2.5 cm; scales and outer tepals essentially entire, often undulate; outer tepals with brownish midstripes to 1.5 mm wide, 4–17 × 4–6 mm; inner tepals pink, oblanceolate, 8–25 × 3–8 mm. Fruits green, drying reddish tan, turbinate,4 × 3 mm. Seeds black, 1.5 × 1–1.2 mm, papillate but not rugose.
Phenology: Flowering spring.
Habitat: Gravel pavements in pinyon-juniper woodlands with mixed sagebrush
Elevation: 2000 m
Of conservation concern.
Pediocactus knowltonii is the smallest and rarest member of the genus. The species is very closely related to P. simpsonii; chloroplast DNA sequence analysis provides support that it represents a recent developmental mutation within P. simpsonii (J. M. Porter et al. unpubl.).