A new fungus of the arbuscular-mycorrhiza forming Glomeromycetes was found in a coffee plantation in Palestina, located in the Amazonian region of San Martín State in Peru. The fungus was propagated in bait cultures on Brachiaria brizantha, Medicago sativa and Sorghum vulgare as host plants. It forms typical acaulosporoid spores laterally on sporiferous saccule necks. The spores are brownish yellow to yellow brown, 125-160 μm in diam and are crowded with papillae on their surface. The papillae are approximately 1 μm wide as well as high. According to the color and surface structure of its spores, the fungus is here described under the epithet Acaulospora flavopapillosa. Phylogenetically, the new fungus clusters in a well-separated clade within a group that comprises A. fragilissima, A. saccata, A. papillosa, A. morrowiae, A. delicata, A. rugosa, A. dilatata and A. longula. Also A. excavata and A. dilatata were found by concomitant morphological and molecular phylogenetic analyses in San Martín State during this study: A. excavata in another coffee plantation, and A. dilatata in an inka nut plantation. An identification key for all species in the family Acaulosporaceae is updated in this study.
