Acaulospora tsugae sp. nov. was found in the rhizosphere soil of the alpine plant Tsuga chinensis var. formosana in Taiwan. It is here presented based on concomitant morphological and molecular spore analyses. The spores of the new fungus are 64–74×84–99 μm in diameter, subglobose to elliptical, pale yellow to yellow, and have three spore walls, which develop inside the neck of a sporiferous saccule. The spores have two persistent opposite cicatrices and differentiate a beaded inner wall that is characteristic for species of the Acaulosporaceae. Based on ITS sequences obtained from the ribosomal gene, a monophyletic clade within a major clade of the Acaulosporaceae is formed, next to several other species that were for the first time detected from montane to high alpine areas in Europe, such as A. alpina, A. pustulata and A. tortuosa. Acaulospora tsugae was also detected at one of multiple sites analyzed in the Swiss alpine regions, suggesting for this conspicuous fungus an infrequent, but intercontinental distribution. An updated identification key for all species in Acaulosporaceae is also included in this study.
