Molecular phylogeny, morphology, mycorrhizal symbiosis, and putative distribution of the arbuscular mycorrhizal fungus Epigeocarpum japonicum (Glomeraceae)

We collected in Japan five sporocarpic specimens morphologically identical to those of Epigeocarpum japonicum, a recently described Glomeromycota species. Although 18S-ITS-28S nuc rDNA sequences obtained from these sporocarps showed high sequence variability, phylogenetic analyses based on 18S-ITS-28S, the largest subunit of the RNA polymerase II (rpb1) gene, and concatenated sequences of the two loci convincingly demonstrated the identity of these sporocarps to E. japonicum. Importantly, the 18S-ITS-28S+rpb1 analyses highlighted the key role of rpb1 sequences in reconstructing the phylogenies of Glomeromycota taxa with strongly divergent rDNA sequences. Upon inoculation with sporocarpic spores, E. japonicum formed mycorrhiza with arbuscules and vesicles, which was not confirmed in the original description of the species. Comparisons of E. japonicum 18S sequences with Glomeromycota DNA sequences available in a public database indicated that E. japonicum is a cosmopolitan species and is mainly associated with plants in natural habitats such as grasslands, shrublands, and forests. Phylogenetic analyses also confirmed the autonomy of E. crypticum, another known species of the genus Epigeocarpum whose sporocarps were originally found in Brazil.