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

Many alpine/arctic flowering plant species have presumably evolved the ability to self-pollinate as a reproductive assurance mechanism under harsh abiotic environmental conditions that restrict insect flower visitation. We compared self-pollination, pollen limitation, insect flower visitation, and dichogamy of low- and high-elevation populations of Cerastium alpinum, a species in established alpine communities, and Cerastium cerastoides, a pioneer species in disturbed habitats. Cerastium alpinum has large showy flowers, while C. cerastoides has smaller and paler flowers. The temporal separation of pollen release and stigma receptivity within a flower (dichogamy) was smallest in C. cerastoides, which was also more highly self-compatible. No pollen limitation on seed set occurred in any species, possibly due to their high selfing ability. Despite a substantially higher pollinator visitation to C. alpinum compared to C. cerastoides, the latter had the higher seed set. Pollen limitation, autogamy, and pollinator visitation did not differ between altitudes for either species. Differences in habitat and flower size, color, and development between the species are consistent with their different selling ability.