Roles played by timing of seedling development and host identity in determining fitness of an annual, subarctic, hemiparasitic plant

Individually mapped plants of Euphrasia frigida, a hemiparasitic annual, were followed for one growing season at a subarctic site in northern Sweden. The strongest factor influencing seed-set was the date when the seedling stage ended, i.e., when plants produced their first noncotyledonous leaves, probably equalling date of attachment to a host. The advantage for early-developing plants was large even with just a 5-d difference in development. A positive effect was caused by presence of the perennial legume Astragalus alpinus, both on seedling development and plant performance, whereas the total cover of nonleguminous herbs or graminoids had no influence on the performance of E. frigida.