Sterile dematiaceous fungi are commonly isolated from plant roots. They are often assigned to Mycelium radicis atrovirens, a name originally proposed for black, sterile, fast-growing, pseudomycorrhizal fungi. Dematiaceous fungi isolated from roots may be mutualists, commensalists, or pathogens and, in the absence of sporulation, identification is not possible. Forty-six isolates of dematiaceous fungi from the roots of different hosts and locations were characterized using restriction site mapping of polymerase chain reaction amplified nuclear ribosomal DNA internal transcribed spacers. The restriction site maps were compared to identified dematiaceous mycorrhizal and pseudomycorrhizal fungi. Computer generated trees (UPGMA and parsimony analysis) characterized two unknown isolates as Phialophora finlandia, an ectendomycorrhizal fungus. The majority of the isolates were characterized as Phialocephala fortinii-like. Phialocephala fortinii has been reported as both pathogenic and non-pathogenic in a number of hosts. There was variation within the P. fortinii-like group suggesting intraspecific variation or a species complex.