General: Mountain Ball Cactus (Pediocactus simpsonii) is a round cactus that grows to about 6-inches tall by 6-inches wide. The stem is covered with long tubercles, central tubercles hairy, each tubercle covered with straight spines. Radial spines 15-35, white, held flat against the body. Central spines 1-11, base white to yellow, tips red, held away from the body.

This species can retract under the soil where it can hide from the brutal heat of summer. In spring, the stem swells and the plant emerges to produce many-petaled, pale flowers. Tepals white to pink to orange. Flowers 1-in long and 2-in wide. Fruit short, cylindrical, flat topped with a cap.

Without flowers, this species can be hard to separate from Spinystar Cactus, but notice that central spines standing out and the different fruit.

Mountain Ball Cactus is a small and inconspicuous, but interesting member of Great Basin and mountain vegetation communities. Look for this species in northern Nevada, north to Montana and east to New Mexico.

Also called Simpson Hedgehog Cactus.