HAMBLETON, SARAH1, RANDOLPH CURRAH1 & KEITH EGGER2.
1Department of Biological Sciences, University of Alberta, Edmonton, AB CANADA. 2Biology Program, University of Northern British Columbia, Prince George, BC CANADA.
The ascomycetous taxa that have been identified as ericoid mycorrhizal fungi are classified in two separate orders; Hymenoscyphus ericae (Leotiales) is an inoperculate discomycete and Oidiodendron maius (Hyphomycete) is inferred to be a member of the Myxotrichaceae (Onygenales). They share several significant characteristics; both produce arthroconidia, form morphologically similar hyphal complexes in root cells, and have been isolated from the same one cm piece of root. Parsimony-based analyses of approximately 1650 aligned nucleotides of nuclear small-subunit ribosomal DNA were used to evaluate whether these ecological and anamorphic similarites indicate a close phylogenetic relationship. Myxotrichum arcticum was included to test the taxonomic affinity of the genus Oidiodendron. The evolutionary relationships of Phialocephala fortinii and "Variable White Taxon" (VWT), two other root endophytes of boreal Ericaceae whose precise ecological roles are unknown, were also examined. A single most parsimonious tree was determined using new sequence data for H. ericae, O. maius, P. fortinii, VWT, and M. arcticum, with GenBank sequences for representatives of the major ascomycete lineages. The hyphomycetes O. maius, P. fortinii, VWT, and the cleistothecial species M. arcticum all clustered with H. ericae in the inoperculate discomycete clade, suggesting descent from a recent common ancester. The other three families of the Onygenales formed a monophyletic clade with the Eurotiales. These results indicate that the Onygenales is polyphyletic as currently circumscribed and that the cleistothecial fruiting body morphology has evolved at least twice. They also suggest that the ability to form mycorrhizas with ericaceous roots may be restricted to fungi with phylogenetic affinity to the Leotiales.