Sclerocactus mesae-verdae
Cactaceae (Cactus Family)

These rare plants are just over an inch high -- with their flowers.

Sclerocactus parviflorus
Cactaceae (Cactus Family)

Semi-desert, foothills.  Woodlands, openings  Spring.
Hunter Canyon Trail, Utah, May 3, 2005.

As this picture indicates, S. parviflorus does produce clustered plants.  It is, however, far more common to find unbranched, solitary stems.  The pictured plants are about seven inches tall.