The type material of Synedra acus var. ostenfeldii Willi Krieg. was investigated using light and scanning electron microscopy. The species is one of the few fragilarioid taxa that forms stellate colonies. Its morphology was compared with that of Fragilaria tenera var. lemanensis Druart, Lavigne & M.Robert, another taxon forming star-shaped colonies, on the type slide and in material from a neighboring lake. The results show both taxa not being conspecific based on valve outline, valve dimensions and presence of spines. Based on the observations, Synedra acus var. ostenfeldii is transferred to the genus Fragilaria as F. ostenfeldii (Willi Krieg.) Van de Vijver, Alexson & Reavie nov. comb. nov. stat. whereas F. tenera var. lemanensis is raised to species level as Fragilaria lemanensis (Druart, Lavigne & M.Robert) Van de Vijver, Ector & Straub stat. nov. Brief notes on their ecology are added.

The genus Fragilaria was originally described by Lyngbye in 1819, although it was only in 1927 that a typus generis was designated by Boyer (1927): Fragilaria pectinalis (O.F.Müller) Lyngbye. Williams & Round (1987), later refined and completed by Tuji & Williams (2006a), provided a detailed description for the genus. Almost all species, nowadays transferred to the genus Fragilaria, were originally described in the genus Synedra Ehrenberg in the nineteenth century. Only a handful of scientists worked on this group then, such as

No abstract