Biological species of theArmillariacomplex present in declining sugar maple stands in southeastern Quebec were identified by pairing monosporous isolates with known tester strains.Armillariaostoyae(I),A.gemina(II),A.calvescens(III), andA.sinapina(V) were collected.Armillariacalvescenswas the most frequent species and was found in almost all the stands sampled. The presence of variousArmillariaspecies was not correlated with either the severity of decline of the stands or the health of the hosts with which they were associated, suggesting that none of the species present in sugar maple stands is particularly responsible for their decline. However, the role ofA.calvescensand the factors that favor its development warrant further investigations because this species appears to be found almost exclusively on maple trees.