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.

Flowering Mar-May; fruiting Nov-May. Chihuahuan desert scrub, desert grasslands, lower edge of oak zone; 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.

Stems 4-9 × 4-10(-15) cm; tubercles 9-20 × 3-7 mm. Spines (8-)14-18(-27) per areole; radial spines (7-)13-17(-26) per areole, abaxial radial spines, needlelike, 6-11(-16) mm diam., stiff; central spines 0.15-0.35 mm diam. Flowers 1.8-2.3 × 1.8-1.9 cm. 2n = 22.

Flowering Mar-Apr; fruiting Aug-Mar. Chihuahuan desert scrub, Tamaulipan thorn scrub, and Edwards Plateau, usually limestone and alluvial substrates; 10-1400 m; N.Mex., Okla., Tex.; Mexico (Coahuila, Nuevo León, Tamaulipas).

The spines of Mammillaria heyderi var. heyderi are smaller and usually more numerous than those of the other flat-topped mammillarias in the United States. Individual plants with fewer radial spines, often segregated as var. hemispherica, are frequent in populations of var. heyderi near the Texas coast. Sometimes the central spines are very short. The coarse western var. bullingtoniana has a much narrower range of variation. Reports of M. heyderi var. heyderi from southeastern Arizona and southwestern New Mexico are based on var. bullingtoniana.