Gymnocalycium nigriareolatum

Gymnocalycium nigriareolatum is a cactus that grows either as a solitary plant or in clusters. It has dull, light to dark gray-green, rounded stems that are 4–6 cm tall and 5–8 cm wide (occasionally up to 12 cm). The plant typically has 10 sharp-edged ribs with shallow, transverse notches. It lacks central spines but has about 7 slightly curved, light gray-brown radial spines with darker tips. These spines are 1–3 cm long, with the 3 lowest being the longest. The flowers are funnel-shaped, either white with a pinkish throat or carmine red. They measure 4–4.6 cm in length and up to 4 cm in diameter. The spherical fruits are small, about 1–1.2 cm in diameter.

This species is native to the Sierra de Graciana and Cuesta de Los Angeles in the Catamarca province of Argentina, where it grows on rocky terrain at altitudes of 500 to 1500 meters.