Gymnocalycium robustum

Gymnocalycium robustum grows as a solitary cactus with gray, gray-green, or slightly mauve-colored, flattened spherical stems. It reaches 8 to 11 cm in diameter and 3 to 5 cm in height. The plant has 9 to 11 broad, flat, blunt ribs that are distinctly cross-grooved and divided into low, chin-like protrusions. It lacks a central spine. There are 5 to 7 stiff radial spines up to 1.5 cm long, one pointing downward and the others sideways. When dry, the spines are chalk-white; when moist, they are yellowish with brown tips and bases. The broad, funnel-shaped flowers are white with a pink throat, measuring up to 6 cm long (occasionally up to 7 cm) and 6 cm in diameter. The fruits are club-shaped or rarely spindle-shaped, gray in color, 4 to 4.5 cm long, and 1.5 to 1.8 cm in diameter.

Gymnocalycium robustum is native to southern Santiago del Estero and Córdoba Province of Argentina, growing on granite rocks at elevations of 300 to 600 meters.