Most of the temperate conifers associate with ectomycorrhizal fungi, but their roots also harbour a wide range of endophytes. We focused on ascomycetes associating with basidiomycetous ectomycorrhizas of Norwayspruce in a temperate montane forest in central Europe and found that the majority of the co-associated fungi belonged to the Rhizoscyphus ericae aggregate (REA), being dominated by Meliniomyces variabilis. We further tested the ability of representative isolates to colonize spruce root tips and European blueberry (Vaccinium myrtillus) hair roots in an agar system as well as their effect on blueberry growth in a peat-agar system. M. variabilis intracellularly colonized spruce (Picea abies) root tip cortex, formed ericoid mycorrhizas in blueberry and enhanced blueberry shoot and root growth in comparison with non-inoculated plants. Our findings suggest that spruce ectomycorrhizas may represent selective niches for ericoid mycorrhizal fungi in habitats lacking suitable ericaceous hosts.