About Acanthocalycium thionanthum (Speg.) Backeb.
Acanthocalycium thionanthum usually grows individually, with spherical to short cylindrical dark green to green-grey shoots. It grows up to 12 cm (4.7 in) tall and 10 cm (3.9 in) in diameter. This cactus has 9 to 15 slightly notched, bumpy round ribs. Elliptical areoles produce appressed gray spines that have darker tips. There are 1 to 4 central spines, which may also be absent, and 5 to 10 radial spines. Its somewhat bell-shaped flowers range in color from bright yellow to red or white. The flowers grow up to 4.5 cm (1.8 in) long, with an equal diameter. The pericarpel and flower tube are covered in dark pointed scales, and brown to white hair and bristles. The spherical, hard-fleshed fruits reach up to 1 cm (0.39 in) in diameter and tear open when mature. Acanthocalycium thionanthum is widespread across the Argentine provinces of Salta, Tucumán and Catamarca, growing at altitudes between 1500 and 3000 meters.
