Same parental species, but different taxa: molecular evidence for hybrid origins of the rare endemics Saxifraga opdalensis and S. svalbardensis (Saxifragaceae)

Saxifraga opdolensis was described from Oppdal in southern Norway and hypothesized to have originated as the hybrid S. cernua × rivularis or to have been derived from a S . cernua-like progenitor. We tested these alternative hypotheses using uni- and biparentally inherited molecular markers observed in S. opdalensis and its putative parental species at the type locality: PCR-RFLPs (restriction fragment length polymorphisms in amplified fragments of chloroplast DNA; cpDNA), sequences of the cpDNA intron trnL and the spacer tmL-tmF , and RAPDs (random amplified polymorphic DNAs). The data provided unambiguous support for the hybrid hypothesis. The cpDNA analyses distinguished two well-differentiated chloroplast genomes, one in S. opdalensis and S. rivularis , and another in S. cernua . The majority of the RAPD markers showed distinct additivity in S. opdalensis relative to its postulated parental species. Thus, S. opdalensis has probably originated from a hybrid with S. rivularis as the maternal parent and S. cernua as the paternal parent. We also included S. svalbaardnsis in the present study because previous molecular analyses of Svalbard material have shown that this species had probably also originated as a hybrid between S. cernua and S. rivularis . The chloroplast genome of S. svalbaardnsis was identical to that of S. opdalensis , but the two species differed in many RAF'D markers. Although these two endemics probably have been derived from the same hybrid combination, they are morphologically and genetically distinct and should be referred to separate species. Differences between such independently originated hybrid taxa may result from intraspecific variation in their parental taxa. Saxufraga cernua comprises, for example, several highly divergent evolutionary lineages.