AbstractA new arbuscular mycorrhizal fungus, Glomus proliferum(Glomales, Zygomycetes) is described. The description, based on a monoxenic culture established in association with a Ri T-DNA transformed carrot root, combines sequencing of the small subunit (SSU) rDNA, spore sterols and fatty acid profiles with more classical taxonomic tools such as optical and electron microscopy. The fungus forms clusters containing hundreds of small, hyaline, four-layered spores. The necessity to use different tools for identification of arbuscular mycorrhizal fungi is discussed.