Potamogeton pectinatus L. × P. vaginatus Turcz. (P. × bottnicus Hagstr.), a newly identified hybrid in the British Isles

A hybrid Potamogeton (Potamogetonaceae) which grows in shallow, rapidly flowing water in the River Till (Cheviot) and River Tweed (Berwickshire (v.c. 81) and Cheviot (v.c. 68 » is apparently referable to P. x bottnicus Hagstr. (P. pectinatus L. x P. vaginatus Turcz.). Both morphological and isozyme characters are consistent with this hybrid combination rather than with the previous identification of these plants as P. x suecicus K. Richt. (P. pectinatus x P. filiformis Pers.). British plants of P. x bottnicus and European plants of P. vaginatus are described and the differences between them, P. pectinatus and P. x suecicus outlined. Possible explanations for the presence of P. x bottnicus in Britain in the absence of P. vaginatus are discussed. The name P. x bottnicus is lectotypified by a syntype referable to P. pectinatus x P. vaginatus. Examination of type material of P. x meinshausenii Juz., described from the vicinity of St Petersburg, indicates that it is not a hybrid between P. pectinatus and P. vaginatus as hitherto supposed