Range and former names
POWO accepts the species in the western and west-central USA. Its range includes Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, South Dakota, Utah and Wyoming. Its basionym is Echinocactus simpsonii. Mammillaria simpsonii was also formerly used. Names with the epithets robustior and minor belong to the synonymy of P. simpsonii in this treatment. Historical use of robustior for P. nigrispinus plants was sometimes a misapplication. [2-WWW] [Heil and Porter 2003a, POWO. Flora of North America, notes on P. nigrispinus]
Stem, flower and seeds
The stem may be spherical, flattened or ovoid, sometimes branched. Typical height and width ranges are 2.5–15 cm, with height exceptionally reaching 25 cm. An areole bears 15–35 white radial spines 3–13 mm long and 4–11 central spines 5–21 mm long. The latter are usually reddish brown with a paler base. Flowers reach 1–2.5 cm in diameter. They may be white, pink, purple or yellowish green. Dry fruits are shortly cylindrical, and greyish-black seeds have a papillose coat. [Heil and Porter 2003a, Flora of North America, P. simpsonii]
Grasslands and higher elevations
Sites include prairies, mountain grasslands, coniferous forests, juniper–pine vegetation and sagebrush scrub. Flora of North America gives elevations of 1400–3500 m above sea level. Flowering occurs in spring and early summer. Within the genus, the species occupies an extensive area and broad elevation range, unlike the narrowly distributed gypsum and limestone cacti of the Colorado Plateau. [Heil and Porter 2003a, Flora of North America, P. simpsonii]
Related articles
Materials from the author's archive
Synonyms and names in the literature
Echinocactus simpsonii · Mammillaria simpsonii · Pediocactus simpsonii var. robustior · Pediocactus simpsonii subsp. robustior · Pediocactus simpsonii var. minor [2-WWW]