Two new freshwater diatom species, Staurosira jolinae and Staurosira circula, are described from the Subantarctic island Ile de la Possession (Crozet Archipelago). Based on their morphological characters, they are placed in the genus Staurosira Ehrenberg. Both species possess a number of typical features that distinguish them from similar taxa such as Staurosira pinnata and Staurosira leptostauron. The two new species are most abundant in small pools in the immediate vicinity of the sea with relatively high pH and moderate specific conductance.