Acanthocalycium thionanthum is a small-sized cactus that naturally grows on South American mountain slopes. Its stem, which can be spherical or cylindrical depending on the age of the specimen, is of a light green or green-blue color. It has downy areoles on the ribs of the plant, from which radial and central spines emerge, which are of a color ranging from white to black. In Greek, 'thionanthum' means 'sulphurous yellow flowers', referring to its splendid bell-shaped flowers of a sulphurous yellow or lemon yellow color (though might be also pink, red, or orange).