Microscopical examination demonstrated that Tricholoma giganteum basidia bear 4 basidiospores. Mating tests revealed that T. giganteum has a tetra-polar, heterothallic mating system. New types of factor B (Br) occurred as a result of recombination within the B-type mating factor. Microscopical examination of that Tricholoma giganteum basidia bear 4 basidiospores. Mating tests revealed that T. giganteum has a tetra-polar, heterothallic mating system. New types of factor B (Br) occurred as a result of recombination within the B-type mating factor.