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

We collected in Japan five sporocarpic specimens morphologically identical to those of <i>Epigeocarpum japonicum</i>, a recently described <i>Glomeromycota</i> 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 (<i>rpb1</i>) gene, and concatenated sequences of the two loci convincingly demonstrated the identity of these sporocarps to <i>E. japonicum</i>. Importantly, the 18S-ITS-28S+<i>rpb1</i> analyses highlighted the key role of <i>rpb1</i> sequences in reconstructing the phylogenies of <i>Glomeromycota</i> taxa with strongly divergent rDNA sequences. Upon inoculation with sporocarpic spores, <i>E. japonicum</i> formed mycorrhiza with arbuscules and vesicles, which was not confirmed in the original description of the species. Comparisons of <i>E. japonicum</i> 18S sequences with <i>Glomeromycota</i> DNA sequences available in a public database indicated that <i>E. japonicum</i> 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 <i>E. crypticum</i>, another known species of the genus <i>Epigeocarpum</i> whose sporocarps were originally found in Brazil.