Genetic relationships of Nuphar in central to western Japan as revealed by allozyme analysis

The genetic relationships of Nuphar japonica, N. oguraensis, N. subintegerrima and two morphologically intermediate plant groups (J-O and J-S) found in central to western Japan were investigated. Allozyme analyses (analysis of allele frequencies and principal coordinate analysis, based on shared allele distance among the 162 multi-locus genotypes) showed the three Nuphar species to be distinguished, and indicated that the intermediate plant groups were genetically intermediate either between two or among three of these species. Natural hybridization and introgression were found to have occurred among these three species in central to western Japan, producing genetically varied intermediate plant groups. Many of the intermediate plants (74.4% of the total numbers of genotypes of the intermediate plants) did not show additive combinations of parental allozymes, which were expected in F1 hybrids. The absence of characteristic parental bands suggested that sexual reproduction had continued among the hybrids beyond the F1.