Single-spore and polyspore cultures of Panellus stypticus from Japan were non-luminescent, while single-spore isolates from Illinois comprised both luminescent and nonluminescent strains. Luminous single-spore isolates exhibited varying levels of luminescence, and in some single-spore isolates, a delay in the onset of luminescence was observed. Japanese and eastern North American collections were universally sexually compatible, and thus belong to the same biological species. Nuclear migration beyond the contact zone between crossed single-spore strains was only occasionally observed, and was consistently accompanied by hyphal lysis of the receptor strain. Production of nuclei fit for nuclear migration appeared strain-specific, and not related to mating type genes.