Acaulospora spinulifera sp. nov. forms spores, which are (74–)84–98(–107) × (73–)77– 93(–98) μm in diameter, yellow brown to brown and ornamented with crowded fine spines formed on the surface of the second, structural, and yellow brown spore wall layer. Phylogenetically, the new species is close to A. baetica, A. cavernata, A. ignota, A. nivalis, A. paulinae, A. punctata and A. sieverdingii, but not to the morphologically more similar species A. spinosissima, A. spinosa or A. tuberculata, that all form larger spores than A. spinulifera. In the A. sieverdingii/paulinae clade, in which currently species with pitted spore surfaces prevail, A. spinulifera is the second species with projections on the structural spore wall layer, besides A. ignota. The latter has warty to flattened elevations in irregular distances on spore surface, which might disappear with age, while the elongated to pointed spines of A. spinulfera are firm and persistent. The new fungus was found in two Cerrado savannas, an Atlantic rainforest, a Caatinga/Cerrado transition zone, and in a soybean production site within the Cerrado.
