Pollination ecology of Gentianella uliginosa, a rare annual of the Dutch coastal dunes

The pollination ecology of Gentianella uliginosa , a rare annual in The Netherlands, was studied in three relatively small coastal dune populations. In all populations, the species was fully self-compatible: manual self pollination resulted in a seed set of 92–94%. Autofertility was also high (seed set of caged, unhandled flowers 80–85%). The homogamous flowers were visited by Bombus pascuorum , which collected nectar and transported pollen sternotribically. Differences among populations in bumblebee visitation rate did not affect natural seed set. In one plot, seed set following natural pollination was lower than after manual selñng, and as high as after spontaneous selñng. As flowers here were also visited frequently, this might be due to pollen limitation through heterospecific pollen competition. Support for this hypothesis was derived from another population, where seed set after natural pollination was lower in a plot dominated by co-flowering Mentha aquatica than in a plot with few Mentha. However, differences in water availability might also have caused this. In one population, seed sets of the cross pollination and spontaneous selfing treatments were lower than those of the manual selñng and natural pollination treatments. Whether the low outcrossing success can be attributed to small differences in the treatment of the experimental plants or to outcrossing depression remains unclear. We conclude that this annual species is most likely a predominant selfer. Its high autofertility is probably an adaptation to its wet dune slack habitat, where reproductive assurance may be important to cope with unpredictable fluctuations in water table, summer droughts and pollinator service.