Accepted name: Ariocarpus retusus subsp. trigonus
Body to over 20 cm wide. Tubercles smooth. Flowers yellow.
Other species without tubercular grooves but with white or pink to magenta flowers include: A. retusus Scheidw. from NE Mexico with tubercles hardly longer than broad; A. agavoides (Castañeda) E.F. Anderson from NE Mexico (Tamaulipas) with a woolly areole above; and A. scaphorostrus Boed. from NE Mexico (Nuevo Leon) which is woolly at the base of the tubercles but without a groove or areole.
Source: (1997). Cactaceae. In: . Horticultural Flora of South-eastern Australia. Volume 2. Flowering plants. Dicotyledons. Part 1. The identification of garden and cultivated plants. University of New South Wales Press.