Reproductive system and population structure in three arctic Saxifraga species

Saxifraga cespitosa, S. tenuis and S. cernua were examined in the Abisko area, N Sweden. Populations of S. cespitosa were gynodioecious. Hermaphrodite individuals showed a high selfing efficiency and low pollen:ovule ratios, consistent with a lower outbreeding rate. Saxifraa tenuis was hermaphrodite with some indication of sexual asymmetry. Pollen:ovule ratios were low, but the ability to set seed by autodeposition was lower in S. tenuis than in S. cespitosa. Saxifraga cernua was androdioecious, with some populations that contained only female-sterile individuals and other populations with both female-sterile and hermaphrodite individuals. The higher production of bulbils by female-sterile individuals, coupled with self-incompatibility in hermaphrodites, suggests a means by which androdioecy may be maintained in S. cernua, in the absence of differences in male reproductive success between gender classes. Although all three species showed significant inter-population differentiation, the morphometric distances between populations were not related to the geographic distances between populations. Most of the total diversity in leaf shape was accounted for by inter-population differentiation in all three species, with