Gymnocalycium denudatum is a species of Gymnocalycium from Brazil to Argentina.
Gymnocalycium denudatum is a solitary cactus with shiny, dark green, depressed spherical stems, 2âÂÂ3 cm tall and 6âÂÂ8 cm wide. It has 5âÂÂ8 flat, minimally bumpy ribs with sparse areoles. Each areole bears 3âÂÂ5 slightly twisted, whitish-yellow spines, 1âÂÂ1.5 cm long, lying close to the stem. The plant produces pure white, glossy flowers up to 5 cm long and 7 cm wide, and elongated green fruits. The species is highly variable.
Native to Brazil (Rio Grande do Sul), Uruguay, Argentina (Misiones, Corrientes), and likely Paraguay, it grows at altitudes up to 500 meters.
Originally described as Echinocactus denudatus by Heinrich Friedrich Link and Christoph Friedrich Otto in 1828, Ludwig Mittler reassigned it to the genus Gymnocalycium in 1844. The epithet denudatum means "naked."