Revision of European Brachysira species (Brachysiraceae, Bacillariophyta): II. The Brachysira styriaca and B. zellensis group

This second paper on the revision of the taxonomic identity of several Brachysira species in Europe deals with Brachysira styriaca (Grunow) R.Ross and B. zellensis (Grunow) Round & D.G.Mann. Both species were described by Grunow based on material from Lake Erlauf (Lower Austria and Styria, Austria). Analysis of type material, additional historic and modern samples showed that most populations of B. styriaca from northern Europe belong to a different taxon. This was already described 70 years ago by Cleve-Euler as Anomoeoneis decipiens A.Cleve and is newly recombined here as Brachysira decipiens (A.Cleve) Van de Vijver & Kusber comb. nov. Brachysira decipiens and B. styriaca can be differentiated based on several morphological and distinct ecological preferences. Brachysira styriaca is typically found in calcium-bicarbonate, oligotrophic, alkaline lakes, whereas B. decipiens prefers acid environments. Brachysira rylandsiana Van de Vijver, D.M.Williams & Ector, sp. nov. is split from Brachysira zellensis based on the parallel valve margins, cuneately rounded apices, and several smaller, ultrastructural details. All species are illustrated with both LM and SEM observations. Their ecological preferences are derived from the accompanying diatom flora in the different investigated samples and the literature.