Body solitary or clustering, to 25 cm tall, 18 cm wide, dark green. Ribs sometimes present. Tubercles bearing areoles at least 1 cm apart, each with a short groove and without nectaries. Central spines 1-7, mostly to about 5 cm long. Radial spines 5-12, mostly to about 1.5 cm long. Flower 3.5-8 cm wide, white, magenta or pink. Fruit green to brown, opening by basal pore.

NE Mexico

There are 3 varieties, the two keyed out being the most readily available.

 

T. heterochromus (A. Weber) Oosten also has large flowers mostly 6-10 cm wide but differs most clearly having rounded tubercles and distinct ribs.

T. hexaedrophorus (Lem.) Britton & Rose from N Mexico has pale green and blue-green stems and flowers white to pale pink.

Source: Thompson, A, ; Forbes, S.; Spencer, R. (1997). Cactaceae. In: Spencer, R.. 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.