Found in southern Brazil,Uruguay, Paraguay, and Northern Argentina, Gymnocalycium horstii is a normally solitary blobular cactus to 8 inches around. Once mature offsets sometimes form. Gymnocalycium horstii looka very similar in appearance to Gymnocalycium denudatum, but it normally has straight spines. Pale pink flowers appear in summer.
     I got this one from Tohono Chul park in Tucson. So far it's fat and happy and gave me a first flower on july 8th 2006. Click below for pictures.

First flower

A close up