An investigation of Achnanthidium (Achnanthidiaceae, Bacillariophyceae) species from Mongolia with the molecular epitypification of A. parallelum

Several strains of Achnanthidium isolated from various water bodies of Mongolia were investigated by light and scanning electron microscopy and molecular genetic methods. On the basis of this investigation, two new species from the A. minutissimum complex are described, A. mongolicum sp. nov. and A. khovsgolense sp. nov. Strains belonging to previously described species A. baicalonanum and A. angustum were also found, expanding our knowledge of the distribution and biogeography of these species. A strain of A. parallelum was studied and designated as an epitype for this species, adding to the reference database of genetic sequences of Achnanthidium taxa, as Achnanthidium is a highly heterogeneous genus with known cryptic diversity in some species complexes, and molecular data are vital in our understanding of its taxonomy. Based on the results of molecular investigation, the relationship between the genera Achnanthidium, Psammothidium and Rossithidium is discussed.