Found in Tamaulipas and Nuevo Leon, Mexico, Ariocarpus retusus ssp. trigonus is one of the largest Ariocarpus forming a ball shaped plant 12 inches across and 10 inches tall. It is a very variable plant, some varieties having short broad tubercules and others long and narrow. Yellowish white flowers are produced in late fall and winter.
     Another Tohono Chul purchase, winter 2006, this plant leaves me just two species short of having all the Ariocarpus.