Polysiphonia subtilissima (Ceramiales, Rhodophyta) from freshwater habitats in North America and Europe is confirmed as conspecific with marine collections

Polysiphoniasubtilissima has a global marine distribution and has been reported from coastlines of every continent except Antarctica. Here, we report P. subtilissima from a freshwater habitat in Pego-Oliva Natural Park, Spain, which is only the third freshwater record for the genus and the first from Europe. This species was previously identified based on morphology from JuniperCreek (Florida, USA), 140 km from marine tidal influence, as well as from a stream on the island of Jamaica. Two molecular markers (5′ cytochrome c oxidase subunit Ibarcode and rbcL) were sequenced for the freshwater collections from Spain and Florida. DNA sequences from the freshwater specimens were identical for each marker and were identical or highly similar to previously published P. subtilissima sequences. Both the freshwater samples were collected from alkaline waters (pH 7.6–8.8 and 7.7, respectively) with high conductivity (1900–2700 and 1840 μS cm−1, respectively) for a freshwater ecosystem, suggesting a high concentra...