Variation
var.denuda     Potato Cactus
This low growing cold tolerant cactus has a dark green globe shaped to spherical stems that turn purplish during winter and grows to 76 mm (3in) tall by 300 mm (12in) wide.

It produces the occasional pale yellow cup shape flowers during early summer and grows in cold conditions to zone-4. This is an excellent rockery specimen plant and is suitable for mountainous regions such as the Colorado Plateau.

Cultivars
'Alberta Sunset'     Spineless Cat's Paw Cactus
This dwarf cactus grows to 100 mm (4 in) tall by 450 mm (18 in) wide, forming a cushion habit with plump rounded spineless pads. It produces bright pink cup-shaped flowers during early summer, followed by dry fruit. It is commonly planted in rockeries and can tolerate very cold conditions to zone-3.

'Black Cat'
This cold tolerant dwarf cactus grows to 150 mm (6 in) tall by 400 mm (16 in) wide with obovate pads that are densely covered in clusters of dark glossy spines. It produces yellow flowers during early summer and can tolerate cold conditions to zone-4

'Nevada Cushion'
This cold tolerant dwarf cactus grows to 100 mm (4 in) tall by 450 mm (18 in) wide forming a very compact cushion habit. It produces occasional yellow cup-shaped flowers during early summer and can tolerate very cold conditions to zone-3