XVI International Botanical Congess

Arbuscular mycorrhizal fungi (Glomales, Zygomycota) have traditionally been classified according to the morphology of their large, multinucleatespores. Six genera in three families have been defined by their mode ofspore formation, and this basic three-family structure has been supportedby previous molecular systematic studies. The existence of several dimorphic fungi that produce spores morphologically belonging to two different families has been difficult to explain in this system. Molecular data reveal that the dimorphic fungi and at least three other species constitute deeply divergent lineages that do not fit into any of the existing families. A new family of the Glomales is currently being described for some of the newly found lineages. These results shed new light on the evolutionary relationships within the group as well as on the evolution of the arbuscular mycorrhizal symbiosis.