Tuberous root connected through a narrow region to the main stem which is to about 6 cm long. Ribs 10-16 and, with the tubercles mostly extremely low. Areoles mostly 1-3 mm wide with central spine absent or solitary and minute, radial spines 0-10. Flowers mostly 1.5-2 cm long.

N Chile

In C. hypogaea var. barquitensis F. Ritter the central spine is not minute but sometimes to 1.5 cm long. [C. barquitensis F. Ritter, invalid]

 

C. laui Diers, from Chile (Esmeralda) is a plant from 1-3 cm tall that is sometimes regarded as a dwarf variant of this species.

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.