Molecular diversity and phylogenetic affinities of symbiotic root-associated ascomycetes of the Helotiales in burnt and metal polluted habitats.

•  The diversity and phylogenetic affinities of symbiotic root-associated ascomycetes of the Helotiales are reported here based on ITS1-5.8S-ITS2 (internal transcribed spacer, ITS) nrDNA sequences. •  Mycobionts were obtained from roots of ericoid plants and grasses and from Piceirhiza bicolorata ectomycorrhizas (pbECM) on conifers and hardwoods, predominantly in burnt and metal-polluted habitats. The mycobionts were sequenced through the ITS and compared with sequences of known helotialean taxa. •  We recognized 132 fungal ITS-sequences with affinity to the Helotiales, of which 75% (54 different ITS-genotypes) grouped within the Hymenoscyphus ericae aggregate including Phialophora finlandia. This aggregate showed stronger affinity to members of the Hyaloscyphaceae and Dermateaceae than to Hymenoscyphus fructigenus (genus-type species; Helotiaceae). Most of the pbECM mycobionts grouped with P. finlandia, although some grouped with H. ericae. Two genotypes co-occurred in ericoid and ectomycorrhizal roots. •  The H. ericae aggregate may be referable to a generic unit, and includes a diverse group of closely related, more or less darkly pigmented, root-associated ascomycetes where the borders between intra- and interspecific ITS-sequence variation, as well as different mycorrhizal and nonmycorrhizal root-symbioses, remains unclear.