Jim Erdman sent this information: Ball or Mountain Cactus (Pediocactus simpsonii) is a common and beautiful cactus you will find throughout Colorado. It is a globular type of cactus reaching up to 6 inches in diameter and is strongly tubercled [meaning rounded projections]. Prickly-pear seems to be more abundant than the Ball or Mountain Cactus, probably because it’s found in more visible masses, especially when in flower.
Mountain cactus flowers from early May to June. These flowers are born in the center of the cactus and are usually a brilliant pink, but can sometimes be whitish in color. Interestingly, the flowers are generally pink on the eastern slope and yellowish on the western slope plants. The flowers usually remain closed on cloudy days.
Mountain cactus is found throughout Colorado, from the foothills to the montane zone. Specimens have even been found at an altitude of 10,000 ft. at Monarch Pass on the western slope – hence the name mountain cactus! Mountain cactus usually grows in rocky soil on exposed ridges where it can receive the most sunlight.
Pediocactus simpsonii was first named by George Engelmann for army engineer James H. Simpson under the name Echinocactus simpsonii. Simpson led an expedition in Colorado, and Engelmann named the species “in honor of the gallant commander” of the expedition. The name of Pediocactus simpsonii was set forth by Britton and Rose, the genus name meaning from the plains (even though this cactus grows in the mountains!).
Pediocactus simpsonii and its variety minor are common in Colorado, and their bright pink flowers make an attractive addition to the Colorado landscape.