Freshwater Benthic Diatoms of Central Europe: Over 800 Common Species Used in Ecological Assessment English edition with updated taxonomy and added species

After the time known informally by diatomists as the “Era of the Green Books” (i.e. the Süßwasserflora) which lasted about until the mid 1990s and during which all the information one needed to have to address the central European diatom microflora was included in four books, there was an explosion of new publications as fundamental concepts underpinning the taxonomy of diatoms were revised, a large number of new species were described, and many familiar taxa bounced between genera. These are exciting times for those interested in the phylogeny, biogeography and diversity of diatoms, but also hugely frustrating times for those concerned with the routine identification of diatoms for practical purposes. Application of the EU-WFD needs a consistent approach to the naming of the organisms upon which assessments depend. Hofmann et al. (2011) represented a welcome exception to the trend of an ever-more diffuse literature on diatoms, since it gave analysts, once again, a single identification text for the species most likely to be found during routine assessments in central Europe. In order to facilitate use outside the German-speaking area, we decided to translate this work into English. At the same time, the lead Editor used this opportunity to update the work to include the latest information on the taxonomy and ecology. Decisions on revisions were made following a very empirical criterion: all taxonomy and ecology papers of which we are aware published until summer 2016 were considered, and all genera and species (if quantitatively relevant) were included if they appeared to be recognized in the main online resources (in particular, ‘Diatoms of the Unites States’, ‘AlgaeBase etc.), and by the community of diatomists. This is a very practical criterion, which might sometimes lead to inclusion of taxa whose merits are still being debated, as long as it appears that they still might have some useful application in everyday practice and some recognition in applied ecology. Following this process, 26 genera were included in the updated English edition of the book whilst in just three cases genera that were included in the first (German) edition have been removed (although they are still mentioned and briefly explained in the book). 10 species have been added to the book, 23 more have been newly mentioned under ‘Similar taxa’, taxonomic concepts were clarified / updated for 36, and 39 were transferred from one genus to another. The clarification and updating made it necessary to produce new identification keys for two genera (Diploneis and Sellaphora). Synthetic information on plastids (only sporadically available in the German edition) has been added whenever possible to the descriptions of the genera. Terminology of both taxonomic features and also ecological concepts was updated in the Glossary. We have also improved the information on ecology and distribution for 22 species. These improvements to the text are accompanied by several additional references. Formal taxonomic changes were carried out only when strictly necessary in order to simplify problematic situations or improve the rationale of genus affiliation: one new species description (of a morphologically distinct Sellaphora of waters of high saprobic level), seven formal transfers (comb. nov.), two formal name changes (nom. nov.). The full text of the species descriptions of the German edition has been replaced by more schematic profiles, in which the different points are provided in a “bullet point” style. This replaces the rich German prose, capable of conveying even nuances of the morphology, with something much far more accessible to international audiences. This English edition, like the earlier German ones, is intended primarily as a tool to facilitate consistent and accurate identification of diatoms in central Europe. We are, however, confident that it might be of general interest for all those looking for an up-to-date overview of most freshwater benthic diatom genera and of the characteristics of their most commonly encountered species.