Sclerocactus sileri, the Siler fishhook cactus, is a rare and very small cactus found mostly in mineral-rich desert areas of intermediate elevations, notably in the American states of Utah, Nevada, and northern Arizona.

The upper central spine is white to tan and is curved and strongly flattened.

[3] Seeds are black to light brown in color, and are 2.2-2.5 mm wide, with a rounded papillae.

The inner tepals are yellow, sometimes suffused with brown, the largest lanceolate, 15–25 mm long and mucronate.

[6][7] The two taxa are treated as two separate species in the Flora of North America, which has entries for: Mistakenly, Anderson (2001) describes only one species, under the name Sclerocactus sileri, treating Pediocactus sileri as a synonym.

[8] His description largely matches the description of Pediocactus sileri in the Flora of North America, and he uses the same common names (gypsum cactus, Siler's pincushion cactus) although the distribution he gives ("a very restricted area in Coconino County, Arizona") corresponds to that of Sclerocactus sileri in the Flora of North America ("restricted to northeast Coconino County, Arizona").

Sclerocactus sileri is a vascular plant, found in habitats including scrubs, forests, grasslands, and especially desert shrubs.

The following plants are usually associated with the Sclerocactus sileri: drop seed (Sporobolus), yucca (Yucca), hedgehog cactus (Echinocereus), sagebrush (Artemisia), snakeweed (Gutierrezia), pinyon (Pinus edulis), and juniper (Juniperus).

Sclerocactus sileri is native to the western United States, and habitat elevations typically range from 850 to 1,650 meters.