Molecular phylogeny of the arbuscular mycorrhizal fungi Glomus sinuosum and Sclerocystis coremioides

We report the first molecular analysis of arbuscular mycorrhizal fungi previously classified in the genus Sclerocystis. Fungi in Sclerocystis sensu lato were distinguished by formation of complex sporocarps. Most species were transferred to Glomus, but both their taxonomic and phylogenetic relations remain the subject of controversy. Phylogenetic analysis of the 18S ribosomal subunit of G. sinuosum (= S. sinuosa) and S. coremioides shows that both species are each other's closest relatives and fall within a monophyletic clade comprising the well-characterized species, G. mosseae, G. intraradices and G. vesiculiferum, to the exclusion of several other Glomus species. This placement indicates that formation of complex sporocarps is an advanced character of some Glomus species, but the sporocarpic trait is not sufficiently unique to group these species into a separate genus Sclerocystis.