The hypothesis that the postfire discomycete Geopyxis carbonaria (Ascomycota, Pezizales, Pyronemataceae) has a biotrophic association with roots of Norway spruce (Picea abies) in nature was tested by isolation of fungal strains from fresh, brown, smooth mycorrhiza-like root tips of Norway spruce collected from below the depth of detrimental heat penetration in a postfire site. The morphology of seven culture isolates originating from the smooth mycorrhiza-like root tips of two different spruce trees was congruent with the morphology of axenic culture isolates obtained from ascospores of G. carbonaria. DNA sequences of the nuclear ribosomal internal transcribed spacers ITS1 and ITS2 from these root-derived cultures and the ascosporic G. carbonaria culture isolates were found to be identical, further supporting the conclusion that the isolates were conspecific. The extensive ascocarp and ascospore formation of G. carbonaria which succeeds a forest fire may be explained in terms of a fungal escape from a moribund tree associate. Possible ecological adaptations of G. carbonaria to the pre- and postfire community are discussed. © 1998 Blackwell Science Ltd.