Although mostly a plant of the Chihuahuan Desert of New Mexico and Texas, echinocactus horizonthalonius
is also found in far south Arizona (the nicholii variety), in and around Organ Pipe Cactus National Monument
, where specimens are generally larger than in the east - up to 12 inches tall. Six inches is more typical. The attractive, slow growing species has broad ribs bearing clusters of (5 to 8) radial spines growing close to the body, and a curved central spine pointing downwards, giving a generally stout, compact appearance. The greenish-gray surface is not obscured by the spines. Bright pink flowers form at the top in early summer, growing out of a dense mat of woolly hairs.