Potamogeton x crassifolius Fryer in the Netherlands

During the summer excursion of the section for investigation of the flora of the Netherlands of the Royal Netherlands Botanical Society Mr H. H. Prell was struck by the appearance of certain Potamogeton leaves, differing from surrounding normal floating leaves of P. natans L. by a brighter green colour, and by their laminae not lying quite flat on the water and being immersed in part. The plant was found July 20th, 1953 in a shallow peaty ditch on the inner side of the dike around the Zuidlaren Lake (province of Drente) at its southeastern corner. The material collected by us agrees almost completely with the description of P. X crassifolius Fryer, Journ. of Bot. 28: 321, tab. 299, 1890.