Pediocactus nigrispinus

Initially spherical, the plant transforms into an egg-shaped configuration as it matures into a densely spiny (often flattened) ovoid form. It grows to 25 centimetres (10 in) tall and from 5 to 15 cm (2 to 6 in) wide. It usually develops into a cluster of ribbed stems, which are 7.5–12.5 cm (3–5 in) wide and green to grayish-blue. There is a characteristic dense arrangement of 4 to 11 large central spines, measuring 1.5 to 2.5 cm (1⁄2 to 1 in) long and yellowish to reddish-brown. There are 15–35 smaller, whitish spines up to 1.5 cm long. The showy pink to magenta flowers appear in the spring and form a cluster near the apex of each stem.

The Columbia Plateau cactus grows in big sagebrush and lower montane dry habitats in eastern Washington and Oregon and extending into Idaho in dry regions, steppes and semi-deserts on hills or rocky outcrops at altitudes between 260 and 1,200 metres (850 and 3,940 ft). It grows in scattered locations but is often locally abundant. Other plants in the habitat include Opuntia polyacantha and O. fragilis.