Taxonomic studies of Achnanthes(Bacillariophyta) in freshwater maritime antarctic lakes

Eleven species of Achnanthes from Signy Island, South Orkney Islands are described including one new species. Benthic algal material from a range of shallow lakes of varying trophic status was examined by light microscopy and scanning electron microscopy. Detail of morphology is provided with an overview of the taxonomic literature for each species. In all cases source descriptions are cited, and where possible holotype and lectotype material was examined. The variation between populations inhabiting different lakes is considered. An examination of the geographical distribution of Achnanthes in southern latitudes from the literature confirms numerous records of widespread occurrence in freshwater environments in sub-antarctic regions but not from higher latitudes.