Molecular evidence for the origin of the little-known hybrid Potamogeton ×vilnensis

A combined study of morphology, stem anatomy, and the genetic markers (ITS1-ITS4 region of nuclear ribosomal DNA and rpl20-rps12 intergenic spacer of chloroplast DNA) was used to verify the identity of hybrid Potamogeton ×vilnensis Galinis previously recognized as P. gramineus × P. praelongus. Authentic herbarium material and newly collected specimens morphologically similar to the hybrid from the locus classicus (SE Lithuania) were used for comparative morphological, anatomical and molecular analyses. The study proved the paternity of P. lucens and P. praelongus and excluded the involvement of P. gramineus in hybridization and identity with P. ×angustifolius. This hybrid formula is shared with plants recorded in the Czech Republic and Denmark under the name P. ×jutlandicus Zalewska-Galosz. The site in Lithuania, known since 1961, is the first natural habitat of long-lived hybrid between P. lucens and P. praelongus whose origin has been confirmed by molecular markers. The scarce records of this taxon indicate that the knowledge of the hybrid species of Potamogeton and their distribution is insufficient and that more extensive regional studies, including molecular methods, are needed.