Morphological Studies of the Armillaria mellea Complex: Two New Species, A. gemina and A. calvescens

The root rot fungus Armillaria mellea in the broad sense represents a complex of different morphological forms. Two new and previously undescribed forms were found to belong to two biological species using mating tests with standard voucher strains. Monosporous cultures from basidiocarps harvested in Québec were compatible with strains of groups II and III corresponding to two new species: Armillaria gemina Bérubé & Dessureault and Armillaria calvescens Bérubé & Dessureault, respectively. They are described and their occurrence and ecology documented. Morphological characteristics of basidiocarps and vegetative isolates can be used to differentiate biological species I, II, III, V, VI and VII found in eastern North America. A key to the A. mellea complex in North America is also presented.