Freely clustering, body globular, crown depressed or flat, to 5 cm wide. Tubercles prominent, conical. Axils naked. Central spines 4-5, 6-7 mm long, lower spine hooked and reddish-brown. Radial spines 30-32, 6-7 mm long, bristle-like. Flowers pink, 1 cm long and wide. Fruit white. [M. mercadensis var. guillauminiana (Backeb.) Repp.]
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.