The former Synedra rumpens complex has long puzzled diatom taxonomists. In the nineteenth century, many infraspecific taxa were described as varieties or forms of S. rumpens. In the present study, type material of Synedra rumpens and several infraspecific taxa such as S. rumpens var. fragilarioides and S. familiaris f. parva and f. major was investigated using LM and SEM observations. For comparison, the original material of several other relevant diatom taxa (such as Fragilaria perdelicatissima, F. spinaspeciosa, Synedra campyla, S. vaucheriae var. distans) was also analysed. The results based on these comparisons show that all infraspecific taxa should be split from Fragilaria rumpens. Fragilaria campyla is a new combination within the genus Fragilaria with F. parva and S. (rumpens var.?) familiaris f. major as synonyms. Fragilaria scotica is likewise a new combina-tion in Fragilaria. Fragilaria metcalfeana is proposed as new name for Synedra familiaris var. neogena. The analysis of F. distans and F. fragilarioides confirmed their conspecificity, with F. fragilarioides having priority as name. Finally, two new species, F. pseudofamiliaris Van de Vijver, T.M.Schuster, Kusber et D.M.Williams sp. nov. and F. bahlsiana Van de Vijver, C.E.Wetzel et Ector sp. nov. are described. Using an analysis of the associated diatom flora, the ecological preferences of each taxon are briefly discussed.