Records of new and rare pondweeds (Potamogeton L., Potamogetonaceae) in the rivers of the north-eastern Central Russia (Kostroma and Kirov Regions)

Records of new and rare pondweeds (Potamogeton, Potamogetonaceae) in the rivers in the north-eastern Central Russia are reported. New localities in Kostroma Region are revealed for P. × angustifolius J. Presl, P. × nitens Web., P. P. × sparganiifolius Laest. ex Fries and P. × suecicus K. Richt. For Kirov Region P. × angustifolius, P. × nitens, P. × olivaceus Baagøe ex G. Fisch, P. × salicifolius, P. × sparganiifolius and P. × suecicus are reported for the first time. For all mentioned pondweeds the distribution, ecology and some other aspects are discussed. The record of a very rare hybrid P. × olivaceus is the first reliable collection for the flora of Russia. The hybrid pondweeds turned out rather widespread and abundant in the studied watercourses, preferring running water ecotopes (riffles, rapids).