ABSTRACTThe population structure ofPeniophora rufawas studied by analysis of somatic and sexual incompatibility behavior. In a plantation ofPopulus tremuloidesin central New York,P. rufaforms populations composed of numerous genetically and physically discrete individuals. Analysis of a single dead limb showed that at least 7 individuals were present. Also, a survey conducted at the plantation to assess the diversity of the basidiomycete community revealed thatP. rufawas the second most common species fruiting on dead aspen limbs.