Breeding system, insect flower visitation, and floral traits of two alpine cerastium species in Norway

The pollination and reproductive ecology of Saxifraga stellaris was investigated in alpine southwest Norway. A breeding system analysis, with performance of controlled crosses, revealed that S. stellaris is self-compatible and that reproductive success after cross- and self-pollination is equal. Relative autodeposition efficiency (i.e. mean seed:ovule ratio in caged, nonmanipulated plants relative to mean seed:ovule ratio of control plants) was, however, low (0.29), suggesting that S. stellaris depends on insect visitation for maximum seed set. Seed set is not restricted by pollen availability, as indicated by a supplemental hand-pollination experiment. Plant size had a strong positive impact on ovule number, which in turn was positively correlated with seed number. Plant size also had a positive influence on seed weight. Seed weight was lowest for late-flowering plants, suggesting that shorter time for seed maturation and lower temperatures late in the season restrict seed weight. No correlations between flowering date and seed number were found, perhaps because the pollinators are relatively insensitive to temperature conditions and thus their activity does not change through the flowering season of S. stellaris