Acaulospora nivalis, a new fungus in the Glomeromycetes, characteristic for high alpine and nival altitudes of the Swiss Alps

A new fungus in the Glomeromycetes was found in the high alpine and nival altitudes of Switzerland in the rhizosphere of several alpine plant species, with a wide soil pH range from 3.9-7.8. It forms bright yellow to dark yellow spores, 81-100 x 75-82 mu m in diameter, laterally on the neck of sporiferous saccules, and has three spore walls. The outer wall is crowded with irregular pits that are 0.9-1.5 x (0.9)1.5-3.5(-5.5) mu m wide and 1.2-2.5 mu m deep. Molecular analyses on the ITS region and partial LSU rDNA gene place the fungus phylogenetically in a monophyletic clade within the genus Acaulospora next to A. sieverdingii, A. paulinae, A. cavernata and A. punctata. An updated identification key for Acaulospora species is presented. The new fungus may co-occur in low frequency with species like A. alpine and A. paulinae in the alpine pastures between 2000 and 2600 m asl. However, it often is the most frequently and most abundantly found Acaulospora species at highest altitudes of plant life, i.e. at subnival and nival altitudes, where it was found in pioneer screes of shallowest soils and associated with pioneer plant species like Linaria alpine, Poa alpine and Saxifraga stellaris.