seems to be especially important in the reproductive isolation of mushrooms, where the clamp connections between the fungal cells that reflect the onset of mating and basidiocarp fructification are almost exclusively observed when the tested mycelia belong to the same species (Le Gac and Giraud, 2008). Such assortative mating has been observed for instance between very close species of the saprophyte mushrooms in the genera Serpula, Hyphoderma, Flammulina and Polyporus, or between related species of the ectomycorrhizal mushrooms Laccaria, Sistotrema and Hebeloma. However, these premating barriers are often weaker when the species do not live in the same geographic area, for instance on different continents. Presumably geographic isolation prevents