Isozyme evidence for the parentage and multiple origins of Potamogeton x suecicus (P-pectinatus x P-filiformis, Potamogetonaceae)

Evidence from isozyme analyses indicates that Potamogeton X suecicus is the hybrid between P. pectinatus and P. filiformis. The hybrid appears to have arisen on several occasions. The isozyme profiles of this hybrid from the Rivers Wharfe and Ure in Yorkshire, south of the present limit of distribution of P. filiformis, suggest that each population is a single clone; these clones may be relies from the Weichselian glacial period. Populations of the putative hybrid from the Rivers Tweed and Till are not P. X suecicus but probably have P. vaginatus and P. pectinatus as parents. If so, this is a remarkable example of a pondweed hybrid persisting vegetatively in an area outside the distributional range of one of its parents.