Mammillaria heyderi var. bullingtoniana
Cact. Succ. J. (Los Angeles) 48: 138, figs. 1, 2. 1976.
Stems 5–11 × 5–12 (–15) cm; tubercles 11–25 × 4–8 mm. Spines usually 10–14 per areole; radial spines usually 10–14 per areole, abaxial radial spines 9–15 mm diam; central spines, when present, 0.35–0.45 mm diam. Flowers 2.2–3.3 × 1.7–3 cm. 2n = 22.
Phenology: Flowering Mar–May; fruiting Nov–May.
Habitat: Chihuahuan desert scrub, desert grasslands, lower edge of oak zone
Elevation: 1200-2100 m
Ariz., N.Mex., Mexico (Chihuahua)
L. D. Benson’s (1982) concepts of Mammillaria gummifera varieties all included material of M. heyderi var. bullingtoniana. The stems, spines, and tubercles of var. bullingtoniana average about one-fourth larger than var. heyderi in all dimensions.