Host affiliation in two subarctic hemiparasitic plants: Bartsia alpina and Pedicularis lapponica

Visual examination of root connections and C-14 labelling were used to identify host ranges of two hemiparasitic angiosperms, Bartsia alpina (L.) and Pedicularis lapponica (L.). Labelling with C-14 was more sensitive than root examination, since seven additional host species and three new host families were found using the former method. In total, is host species belonging to 11 families were found. Most of the hosts were members of the Cyperacene, Lentibulariaceae or Liliaceae. Not all species tested using C-14 labelling were found to be hosts, and there was no preference for host species with large root systems. Both hemiparasites formed connections with Pinguicula vulgaris, which has a very small and stunted root system compared with the root system of larger plants such as Betula spp. We conclude that the mere presence of another species growing close to a hemiparasitic plant does not mean that this plant is used as a host.