Staurastrum sinense was found in a pool in Flanders (Belgium) in 2020. The cells were all 4-radiate. In a preserved sample, after a year, (dead) 5-radiate forms of Staurastrum sinense were also found, hitherto unknown in the literature. Further investigation in the same pool did not reveal a single 5-radiated cell. Can such a form only arise 'in vitro'?