Abstract
The aim of this study was to identify the habitat requirements and host specificity of three root parasites in the genus Thesium (T. linophyllon, T. bavarum and T. ebracteatum). We conducted a vegetation survey and tested whether some plant species occur more often in plots with Thesium spp. than expected, thereby representing potential hosts of the parasites.
To test if the potential hosts are the species to which Thesium is physically attached, we also conducted an excavating and sowing experiment. We found a positive association with surrounding species for T. linophyllon, but not for the other two species.
The number of haustoria of T. linophyllon attached to roots of host species was affected by the number of roots of the surrounding species and by their identity (species, family and plant group). Thesium was, however, attached to 94% of all species occurring in the plots.
We suggest that Thesium spp. do not specifically select hosts, but rather occur in microhabitats with specific conditions.