Hybridization ofSaxifraga oppositifolia andS. biflora (Saxifragaceae) in a mixed alpine population

Saxifraga oppositifolia, S. biflora, and their hybridS. ×kochii were studied in a mixed population in the Swiss Alps. Qualitative morphological characters did not allow to clearly separate the hybridS. ×kochii from its parental species. All quantitative characters were intermediate inS. ×kochii, but the ranges of these characters overlapped with those ofS. oppositifolia andS. biflora. A hybrid index and canonical discriminant analysis allowed a clear separation of the three groups and strongly confirmed a priori grouping. Phenological observations showed that the three groups were not temporally separated within the investigated mixed population. Reciprocal hand pollinations betweenS. oppositifolia andS. biflora yielded higher seed set withS. oppositifolia than withS. biflora as maternal plant. Germination rate of seeds from these crossing experiments varied in the same way as seed yields, whereas germination rate was intermediate for seeds from naturally pollinatedS. ×kochii. Considering its ecological and reproductive properties,S. ×kochii has good prerequisites for evolving into a distinct species.