Otospora bareai, a new fungal species in the Glomeromycetes from a dolomitic shrub land in Sierra de Baza National Park (Granada, Spain)

A new fungal species of the Glomeromycetes was isolated from the rhizosphere of Pterocephalus spathulatus and Thymus granatensis, two rare endemic plants growing on dolomite in the Sierra de Baza (Granada, southern Spain). The fungus was propagated in pot cultures of Sorghum vulgare and Trifolium pratense for 4 y and it is described here on the basis of the spores found in nature and formed in pot cultures. Its brown spores (140-210 km diam) form laterally on a persistent, brown stalk (=neck) of a sporiferous saccule. They have two walls without ornamentation: a brown, three- to four-layered outer wall and a hyaline two- to three-layered inner wall. The unique combination of spore formation and spore wall structure does not fit with any of the known fungal genera. Spore formation is similar to that of Acaulospora spp. and Archaeospora trappei, but Acaulospora spp. has three spore walls with a characteristic "beaded" wall, and the outer wall of Ar. trappei is simple, thin, hyaline and only bilayered. Spore wall structure of the new fungus is similar to that of Entrophospora infrequens, however this fungus forms its spores internally, inside the hyphal stalk of the sporiferous saccule. Molecular analyses of the small subunit of the ribosomal gene phylogenetically place the new fungus next to Diversispora spurca, which forms one-walled glomoid spores (i.e. terminally on hyphae). Based on these analyses we place the new fungus into a new genus in the family Diversisporaceae under the epithet Otospora bareai.