[2] Gymnocalycium stenopleurum is a cactus species with gray-green, flattened, or spherical stems reaching up to 12 cm tall and 6–12 cm wide.

It has 8–14 rounded ribs and 3–6 twisted, light to dark brown radial spines measuring 0.7–4 cm long, while central spines are typically absent.

The plant produces white flowers 5–7 cm long and gray-green fruits up to 4 cm long and 1 cm wide.

[3] Native to Cerro León in Paraguay's Boquerón department and eastern Bolivia, it grows at altitudes of 10 to 500 meters.

[4] Friedrich Ritter first described the species in 1979.