4. Gymnocalycium Pfeiffer ex Mittler (1844:124)

Type (designated by Haworth 1816: 137):— Gymnocalycium gibbosum (Haworth 1816: 137) Pfeiffer ex Mittler.

Species richness:— Gathers approximately 50 species, four species occur in Rio Grande do Sul (Kiesling 2005).

General distribution:— Gymnocalycium is distributed in southern Brazil, Uruguay, Argentina, Paraguay, and Bolivia.

Distribution in Santa Maria river basin:— Two species were found, Gymnocalycium denudatum (Link & Otto 1828: 9) Pfeiffer ex Mittler (1844: 124) (Fig. 2K), and G. uruguayense (Arechavaletae 1905: 218) Britton & Rose (1922: 172) (Fig. 2L), they are widespread in the study area and grow on rocky outcrops and the Saxon vegetation, tolerate low light.

Morphologic notes:— These are usually solitary or clustered plants, globose of more than 4 cm in diameter, 4–15 sides, bell-shaped, white calyx, pink or yellowish-white flowers. Dried or fleshy fruits up to 3 cm in length. They usually bloom from October to December, bearing fruit soon after.