Sieverdingia gen. nov., S. tortuosa comb. nov., and Diversispora peloponnesiaca sp. nov. in the Diversisporaceae (Glomeromycota)

Phylogenetic analyses of 18S-ITS-28S nuc rDNA sequences indicated that the arbuscular mycorrhizal fungus originally described as Glomus tortuosum and later transferred to the genus Corymbiglomus represents a separate, previously unrecognized clade at the rank of genus in the family Diversisporaceae (order Diversisporales, phylum Glomeromycota). The analyses located the clade between clades representing the genera Desertispora and Redeckera. Consequently, a new genus, Sieverdingia, was erected, with S. tortuosa comb. nov. The unique morphological feature of S. tortuosa is the formation of glomoid-like spores with a single-layered spore wall covered with a hyphal mantle. Importantly, the erection of Sieverdingia clarified the definition of Corymbiglomus, which currently consists of three species producing glomoid-like spores with one, three- to four-layered spore wall. The features of the innermost layer, which is hyaline, laminate, flexible to semi-flexible, indicate that it is a synapomorphy of Corymbiglomus. The definitions of Corymbiglomus and its species were emended. Moreover, the distribution of S. tortuosa and the three species of Corymbiglomus was discussed based on own studies, literature data, and molecular sequences deposited in public databases. We concluded that the distribution of S. tortuosa and C. globiferum known in environmental studies based on their partial 28S nuc rDNA sequences only may be understated because the main molecular characteristics distinguishing these species reside outside the 28S region. Finally, we described a new species in the genus Diversispora originating from Mediterranean dunes of the Peloponnese peninsula, Greece. The same phylogenetic analyses mentioned above indicated that the closest relative of the new species, producing dark-coloured spores, is D. clara, whose spores are creamy white at most.