Neotypification of Potamogeton ×fluitans Roth and the distribution of this hybrid

The identity of the name Potamogeton fluitans Roth has for a long time been uncertain. An analysis of the history of the name and its use is presented and the identity of the extant material ascribed to Roth discussed. The name P . fluitans is neotypified with a specimen from a population of the hybrid P . lucens L. × P . natans L. recently studied morphologically, anatomically and electrophoretically. Nomenclature of the hybrid is summarized and lectotypes for a further four names designated. Distribution of the hybrid is described and a list of representative specimens given.