The Achnanthidium minutissimum complex (Bacillariophyceae) in southern Poland

Representatives of the Achnanthidium minutissimum (Kutz.) Czarn. complex are common and widespread diatoms in Poland. The following species were included in this study: Achnanthidium affine (Grunow) Czarn., A. caledonicum (LanGe-Bert.) LanGeBert., A. eutrophilum (LanGe-Bert.) LanGe-Bert., A. exile (Kutz.) HeiB., A. jackii raBenH., A. lineare w. Sm., and A. minutissimum. Two additional species are here formally described, namely Achnanthidium polonicum Van de VijVer, wojtaL, e. moraLeS et eCtor and A. acsiae wojtaL, e. moraLeS, Van de VijVer et eCtor. Information for an additional taxon is presented here, but it has been left unidentified until a larger population is found. Results of morphological analyses performed with light and scanning electron microscopy on this group of diatoms inhabiting springs, streams, rivers and lakes in southern Poland are illustrated and briefly discussed. Distribution of Achnanthidium caledonicum, A. eutrophilum, A. exile, A. lineare and A. minutissimum in waters of southern Poland corresponds well with literature reports of their autecology.