Discovery of a new, recurrently formed Potamogeton hybrid in Europe and Africa: Molecular evidence and morphological comparison of different clones

A new Potamogeton hybrid resulting from crossing between P. nodosus and P. perfoliatus, and occurring in Europe and Africa is described here as P. ×assidens. The hybrid identity was unequivocally confirmed by molecular study of ITS and selected chloroplast DNA regions. In European populations, for which the maternal taxon was identified based on cpDNA as P. nodosus, maternally driven expression of characters may account to a large degree for shaping the range of morphological variability of the hybrid taxon. This was accompanied by a matroclinal concerted evolution observed at the molecular level in the ITS sequences. Our observations may suggest the presence of some genetic mechanisms that promote a higher impact of the maternal lineage on the expression and evolution of the hybrid variability both at the molecular (direction of concerted evolution in hybrids) and the morphological level. Distinctive characters of P. ×assidens and other morphologically close Potamogeton hybrids are discussed. The hybrid most similar to P. ×assidens, namely P. ×rectifolius, is typified.