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

Saxifraga opdalensis was described from Oppdal in southern Norway and hypot hesized to have originated as the hybrid S. cernua x rivularis or to have b een derived From a S. cernua-like progenitor. We tested these alternative h ypotheses using uni- and biparentally inherited molecular markers observed in S. opdalensis and its putative parental species at the type locality: PC R-RFLPs (restriction fragment length polymorphisms in amplified fragments o f chloroplast DNA; cpDNA), sequences of the cpDNA intron tmL and the spacer tmL-tmF, and RAPDs (random amplified polymorphic DNAs). The data provided unambiguous support for the hybrid hypothesis. The cpDNA analyses distingui shed two well-differentiated chloroplast genomes, one in S. opdalensis and S. rivularis, and another in S. cernua. The majority of the RAPD markers sh owed distinct additivity in S. opdalensis relative to its postulated parent al species. Thus, S. opdalensis has probably originated from a hybrid with S. rivularis as the maternal parent and S. cernua as the paternal parent. W e also included S. svalbardensis in the present study because previous mole cular analyses of Svalbard material have shown that this species had probab ly also originated as a hybrid between S. cernua and S. rivularis. The chlo roplast genome of S, svalbardensis was identical to that of S. opdalensis, but the two species differed in many RAPD markers. Although these two endem ics probably have been derived from the same hybrid combination, they are m orphologically 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. Saxifraga cern ua comprises, for example, several highly divergent evolutionary lineages. (C) 2000 The Linnean Society of London.