Hidden complexity: An assessment of species diversity within the genus Discostella (Bacillariophyta)

The centric diatom genus Discostella is common in freshwater communities worldwide. Sixteen extant species are currently known, many of which are morphologically very similar. In applied taxonomy mostly broader concepts of D. stelligera and D. pseudostelligera are used. To assess the species diversity of the genus, 58 strains were cultivated and investigated using morphometric and molecular methods, obtaining the first multi -gene phylogeny of Discostella. Up to 22 operational taxonomic units were identified. For the taxonomic assignment of the OTUs a detailed morphological analysis including several type materials was performed. Up to 15 OTUs did not fit any existing taxon, revealing previously undetected diversity in the genus. A comparison of the different molecular markers revealed hints of a more complex intrageneric structure possibly due to reticulate evolutionary processes. The identity and generic placement ofD. glomerata is resolved and D. angainor sp. nov. is described.