The genus Stauroforma was first described by Flower et al. (1996 in Diatom Res. 11) to accommodate a former variety of Fragilaria virescens Ralfs (now in the genus Fragilariforma), because it lacked a rimoportula. However, the taxonomic history of Stauroforma exiguiformis is far from being clear, mainly because of confusion about the valid publication of the basionym F. virescens var. exigua. A second species, S. inermis, was placed in Stauroforma based on samples from the Maritime Antarctic Region. These species differ with regard to linking spines (present in S. exiguiformis, but absent in S. inermis) and the formation
of long chain-like colonies in S. exiguiformis while S. inermis is only present as solitary cells. In the present contribution, we unravel the taxonomic history of F. virescens var. exigua by examining Grunow’s original drawings and several historic Grunow samples containing the
taxon. Different Antarctic populations of S. inermis were added to the analysis and compared with its presumed European records, showing that, in our opinion, these European populations should be split from the Antarctic taxon. Additionally, two other varieties of F. virescens described by Grunow, such as var. oblongella and var. subsalina, havebeen analysed. Based on this, F. virescens var. subsalina belongs to the genus Stauroforma and can be considered identical to the European records of S. inermis, but is different from the Antarctic populations. The analysis of the different populations and taxa indicated that the current concept of the genus Stauroforma should likely be modified by
its circumscription, as currently only S. exiguiformis fits this description, whereas all other Stauroforma taxa differ markedly in having mantle striae and apical pore fields, but lacking linking spines almost completely.