Strombocactus disciformis

Strombocactus is a monotypic genus with a strong turnip-like root, a small, depressed, roughly spherical stem covered with spirally arranged overlapping tubercles, each with a spine-bearing areole at its tip. Strombocactus disciformis are low-growing, gray-green succulents with a broadly round, unbranched stem and root. In their natural habitats, they grow in a disk shape, half hidden in the ground, reaching around 8 cm in diameter and 2-3 cm in height. In cultivation, they become nearly spherical. Adult tubers can reach 15 cm in diameter, larger than the above-ground parts. The plant's spiral ribs are deeply notched, creating a wart-like appearance with a ratio close to the golden ratio (13:8). Areoles are located on the blunt ends of these warts, which are curved (straighter in cultivation) and have a square base. They rarely have more than four or five short, bristly thorns, which fall off after a few years. Flowers come from new growth at the crown, emerging from the youngest areoles. The flowers are white to cream or magenta and 2.5- to 3.5-cm long and open to about 4 cm in diameter. The 7-mm-long, thin-walled brown fruits contain 0.3-mm reddish-brown seeds.

Strombocactus disciformis is found in the Mexican states of Querétaro, Hidalgo, and Guanajuato, growing on almost vertical, weathered limestone rocks at altitudes of 1000 to 1600 meters.