The number of arms (processes) within Staurastrum is known to be variable, even within a species. In a pool in Flanders (Belgium) a form of Staurastrum boreale was found with six arms on both semicells. Further investigation in a very nutrient-rich other pool with Staurastrum boreale revealed that here 9 combinations of this species were present with regard to radiality. The question is raised whether such a large variation could be related to the high nutrient richness in this pool.