Gymnocalycium saglionis is probably the largest of Gymnocalyciums. Solitary, globular, even flattened when young, it gradually becomes columnar as it ages. In the wild in Argentina it can get to be 12 inches around and 3 feet high. I hope mine in the garden takes it's time getting that big! It's allready about 5 inches around. Though I've never seen any, it is supposed to produce white flowers with a pink tinge throughout the growing season. I think mine doesn't get enough sun to bloom.

The smaller one in my garden

First flower from the one in the garden

Multiple buds on the big guy

Seven flowers at the same time