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

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