Rhizoglomus venetianum, a new arbuscular mycorrhizal species from a heavy metal contaminated site, downtown Venice in Italy. Rhizoglomus venetianum

Rhizoglomus venetianum, a new arbuscular mycorrhizal species was isolated and propagated from a heavy metal contaminated site on the Sacca San Biagio island, downtown Venice in Italy. Interestingly, under the high levels of heavy metals on the Sacca San Biagio island, the new fungus appeared to grow entirely intraradical. In greenhouse trap and single species cultures under low heavy metal levels, it formed innumerous spores, clusters and sporocarps also extraradically, which are formed terminally on subtending hyphae either singly, in small spore clusters, or, preferably, in loose to compact non-organized sporocarps up to 2500 × 2000 × 2000 µm. Spores are golden-yellow to bright yellow brown, globose to subglobose to rarely oblong, 75-145 x 72-140 µm in diameter and has four spore wall layers. Morphologically, it is most similar to R. intraradices, but phylogenetically, it forms a monophyletic clade next to R. irregulare, which generally forms irregular spores and lacks, like R. intraradices, the flexible innermost wall layer beneath the structural/persistent third wall layer. A key for the species identification is presented comprising all 18 Rhizoglomus species, so far described or newly combined.