Mountain Ball Cactus

The body of this succulent plant is one or more enlarged rounded stems, 2.5–15 centimeters wide and 2.5–25 centimeters tall, though it usually is less than 15 centimeters in height. The shape of this stem is like an egg with the wider part towards the soil (ovoid) or like a ball shape (globose), but can be flattened out or sunken into the ground in appearance (depressed), particularly in winter. The surface of the plant is covered in pyramid shaped projections or branch-lets called tubercles. At the tip of each tubercle a round to oval structure 3 millimeters across called an areole. It is covered in fine hairs (villous) and is where the cluster of spines grow. The spines are quite hard and smooth and vary in color and size by position. The spines at the center of the cluster number 4 to 11, are 5–21 millimeters long, and are a dark color such as reddish-brown or even black at the ends with a cream to yellow colored base. The spines arrayed around the center (radial) number 12 to 35 per cluster, are 3–13 millimeters long, and are white in color.

Flowering and fruit. Pediocactus simpsonii has its flowers are grouped at the center-top of the stem and are surrounded by brown or white woolly hairs. The flower buds are blunt shaped. …

Pediocactus simpsonii is found throughout the interior western United States from Arizona and New Mexico in the south to Idaho and Montana in the north. It can also be found in Nevada, Utah, Wyoming, Colorado, and South Dakota. In Montana it is only found in the mountains in the southwest of the state near to the border with Idaho. It if found throughout much of the southern, non-panhandle, portions of Idaho, excluding only the western edge. In Wyoming it grows in the southern and the western sides of the state. In Nevada it is found in the mountain ranges of the Great Basin in the eastern side of the state. Utah's populations can be found through much of the state where suitable habitat is found. In Colorado it grows in the foothills, mountains, and west slope of the state. It is found only in a few isolated populations in northern Arizona and is likewise found only in the mountains of northern New Mexico. In 2013 NatureServe evaluated the species and found it to be globally secure, G5. At the state level they evaluated it as apparently secure (S4) in three states, Montana, Nevada, and Utah. In three other states, Idaho, New Mexico, and Wyoming it was evaluated as vulnerable (S3). They found it to be critically imperiled (S1) in Arizona and have not evaluated its status in Colorado or South Dakota. …

The attractiveness of the "beautiful flowers" is noted even botanical texts and so mountain cactus is a plant desired by gardeners for use in rock gardens in cold climates. When grown in a garden setting the mountain cactus requires a loose soil that will not set too hard when it dries. Plants survive well with a growing medium that is two-thirds sand and one-third rotted leaves, with a layer of pure sand around the base of the plant. Rotting may occur if water remains around the plant. Flowering is reduced if mountain cactuses are not kept dry and cool during the winter season. Though very hardy in cold climates, these cactuses will die if transplanted to a hot desert climate. Germination studies on mountain cactus seeds indicate some need of cold-moist stratification. Only 10% of seeds germinated at 21 °C after eight weeks where on the other hand 67% germinated at 4.5 °C in 17 days. Further tests found that the growth hormone gibberellic acid (GA3) would stimulate 70% germination of seeds that had been stored for several months when planted at 21 °C and even a sample that had been stored for around two years would sprout at 33% when treated with GA3. In contrast seeds stored for several months and planted at 4.5 °C and then raised to 21 °C only showed an 18% germination rate in 2–10 weeks.