Discovery of the Northern Hemisphere hybrid Potamogeton ×salicifolius in the Pilbara region of Western Australia

The interspecific hybrid Potamogeton ×salicifolius (= P. lucens × P. perfoliatus), so far known only from several countries of Europe and a few countries of Asia, was discovered in Western Australia. Morphology of the Australian specimens fits the variation range of the Eurasian specimens. DNA sequencing confirmed the morphological identification as a hybrid P. lucens × P. perfoliatus and identified the former species as the maternal one. This identity is surprising because none of the parental species are known to occur in Western Australia and P. lucens currently even does not occur in the continent. Three possible explanations for the occurrence of P. ×salicifolius in Western Australia are discussed: its relictual occurrence from the time when both the parental species occurred there, long-distance dispersal of a hybrid seed from Eurasia and the remnant of local cultivation or intentional planting.