It is a native of Uruguay and E. Argentina where an occasional -12 C (10.4F) frost sometimes occur. Reliable information reports 'Alberto Castillo' having survived impervious -24 C (-11.2 F) temperatures in the States. Of course it is not what it would prefer coming from a sunny part of the world with mostly mild winters. 'Rolf Fedler' does come from a tiny part of Uruguay where South African conditions are the rule. Oddly enough, in a matter of a couple of decades and perhaps from seed propagation, 'Rolf Fiedler'in cutivation is a lot hardier than the original material. 'Rolf Fielder' does not cross with I. uniflorum. Sadly for us it seems the name to be used is Tristagma uniflorum as there is nothing to separate the two genera on reasonable grounds and Tristagma is prior.