MOLECULAR EVIDENCE FOR POLYPLOID ORIGINS IN SAXIFRAGA (SAXIFRAGACEAE)- THE NARROW ARCTIC ENDEMIC S-SVALBARDENSIS AND ITS WIDESPREAD ALLIES

The recently described polyploid Saxifraga svalbardensis is endemic to the arctic archipelago of Svalbard. We investigated relationships amo ng four closely related species of Saxifraga in Svalbard and tested th ree previously proposed hypotheses for the origin of S. svalbardensis: (1) differentiation from the morphologically and chromosomally variab le polyploid S. cernua; (2) hybridization between the diploid S. hyper borea and S. cernua; and (3) hybridization between the tetraploid S. r ivularis and S. cernua. Fifteen populations were analyzed using random amplified polymorphic DNAs (RAPDs) and nucleotide sequences of the ch loroplast gene matK and the internal transcribed spacers (ITS) of nucl ear ribosomal DNA (rDNA). RAPD and matK data suggest that S. svalbarde nsis has originated from a hybrid with S. rivularis as the maternal pa rent and S. cernua as the paternal parent, possibly a single time, whe reas ITS data could not be used to discriminate among the hypotheses. The data also suggest that the diploid S. hyperborea is a progenitor o f the tetraploid S. rivularis. The four populations examined of S. sva lbardensis were virtually identical for RAPD and ITS markers, whereas S. cernua showed high levels of variation, suggesting that the latter polyploid either has formed recurrently or has undergone considerable differentiation since its origin.