GENETIC-VARIATION AND HYBRIDIZATION IN SWEDISH SCHOENUS (CYPERACEAE)

Schoenus ferrugineus and S. nigricans have restricted distributions in Sweden and are almost exclusively confined to calcareous fen habitats . At S. nigricans sites, S. ferrugineus is usually also present, and h ybrids are frequently found. In this report, I used allozymes to estim ate the amount of gene flow between the two species, and to compare th e partitioning of genetic diversity in each of them. Thirteen loci wer e analysed at eight different enzyme systems. Seven loci were variable between or within the species. The two species had completely differe nt alleles at two of the seven variable loci, whereas there was overla p at five loci. In all, 22 different alleles were found. Six of these alleles were confined to S. nigricans, and five alleles were confined to S. ferrugineus. Nei's genetic identity was 0.55. - In S. ferrugineu s, three loci (23%) were polymorphic, and the average number of allele s per polymorphic locus was 2.0 (each polymorphic locus had two allele s). In S. nigricans, three loci (23%) were polymorphic, and the averag e number of alleles per polymorphic locus was 2.3. - The proportion of genetic diversity due to variation among sites (C-ST) was fairly simi lar in the two species, mean over loci = 0.12 in S. ferrugineus and 0. 15 in S. nigricans. However, the proportion of genetic diversity due t o variation among individuals within sites (G(IS)) differed markedly b etween the two species, mean over loci = 0.54 in S. ferrugineus and 0. 17 in S. nigricans. Accordingly, there was a much higher individual he terozygosity in S. nigricans than in S. ferrugineus. - Most hybrids we re interpreted as F-1 hybrids. However, a small proportion, 0.5-1.6%, were F-n hybrids or back-crosses. - On the Swedish mainland, all forme r occurrences of S. nigricans are extinct, but viable hybrids are stil l present at a few sites in southernmost Sweden.