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Colorado Hookless Cactus
These portly cacti shrink into the ground during droughts, making them often difficult to find.
About This Species
The Colorado hookless cactus was federally listed as threatened in 1979. In 2023, genetic analysis revealed that populations once thought to all be Colorado hookless cactus were actually two different species, Sclerocactus glaucus (still known as Colorado hookless cactus) and Sclerocactus dawsoniae (now known as Dawson's hookless cactus). In 2025, the Colorado hookless cactus (the two species were treated as one species under the federal listing) was removed from the Federal List of Endangered and Threatened Plants due to its recovery.
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Physical Characteristics
Colorado and Dawson’s hookless cacti are small, squat, spherical plants with a dull gray-green stem. The stem can grow up to 5 inches tall and has vertical ribs, each with multiple areoles (bump-like raised areas) adorned with spines. While its radial spines (spines that stick out the sides of the areoles in a star-like pattern) are hooked, the central spines (which stick straight out) are not hooked, which distinguishes these two species from others and gives them their "hookless cactus" name. During dry times, the stem can shrink below the surface of the ground; this helps cacti retain water and protects them from UV radiation, but makes them hard to find. From April to May, hookless cacti display showy, bright pink flowers with yellow stamens (the tube-like structures at the center of a flower).
Range
Colorado hookless cacti are found in arid shrublands on the Western Slope of Colorado. Sclerocactus glaucus is found in Delta, Montrose and Mesa Counties, while Dawsin’s hookless cactus is found only in Garfield County. The elevation range of these species is 4,603 to 7,152 feet.
Habitat
These cacti are found in rocky areas in the desert shrublands of western Colorado. They often grow on hot, south-facing slopes above the Gunnison and Colorado rivers and their tributaries. The soils they grow in are usually dominated by large volcanic cobbles and pebbles.
Colorado and Dawson’s hookless cacti often grow with woody desert plants including shadscale (Atriplex confertifolia), galleta grass (Hilaria jamesii), black-sage (Artemisia nova) and Indian rice grass (Eriocoma hymenoides).
Threats to Species
Oil and gas development, motorized and nonmotorized recreation, and excessive grazing can damage the fragile habitats where these cacti occur. A demographic study conducted from 2011 to 2017 found that the largest cause of cactus deaths was herbivory by small mammals.