Pediocactus sileri is an exceptionally rare plant long cherished as a Utahia sileri and found to be rather difficult in cultivation, but nevertheless much sought after. It is a solitary or, less commonly, few-branched cactus measuring up to to 25 cm tall and nearly 12 cm in diameter, making it one of the larger plants in the genus. It is similar to Pediocactus simsonii, but all of the spines have thick bases. 3 central, erect spines are brown or blackish, but lighten to a white colour with age, while the 8-15 radial spines are similar to the central ones but white or pale grey and about half as long straight or slightly curved. Although numerous, the spines only hide about half of the blue-green stem. During the spring, bright greenish yellow flowers about 2.5 centimeters in diameter will bloom and produce greenish yellow fruit. This plant does not shrink significantly in summer or winter as so many other plants in this group do.