Aspects of reproduction in Cerastium alpinum on calcic and ultramafic soils in Central Norway

Cerastium alpinum is one of several species of Caryophyllaceae able to grow on soils of deviating chemical composition, including ultramafic soils. To compare mating systems between plants growing on calcic and ultramafic soils, pollination experiments were performed in one ultramafic and four calcic sites in Central Norway. Two populations on calcic soils were classified as ssp. lanatum and two as ssp. alpinum. The results suggest that C. alpinum is a highly self compatible mixed mater with a large proportion of facilitated selfing. Plants on different soils showed no significant difference in mating system. However, relative seed set and number of initial ovules differed. The population on ultramafic soil produced a significantly lower number of initial ovules than those on calcic soils. Relative seed set was also lower on ultramafic soil. The difference in number of initiated ovules, along with known differences in various morphological traits, i.e. plants on ultramafic soils display a mon dwarfed stature, suggest that plants on ultramafic soils allocate more resources to survival than to reproduction and growth compared to plants on calcic soils. In addition, on calcic soils a higher relative seed set was found in ssp. lanatum than in sap. alpinum, probably caused by habitat differences between the investigated populations rather than by genetic differences between the two taxa. The obvious success of C. alpinum on ultramafic soils may partly be ascribed to easy establishment in this scarcely vegetated habitat.