A SEM study of the nivicolous taxa belonging to the Diderma niveum complex including the six previously described taxa D. alpinum, D. cristatosporum, D. microcarpum, D. niveum, D. niveum var. ferrugineum and D. niveum var. macrosporum is presented. Type collections of Rostafinski and Meylan were examined. New lectotypes for Diderma alpinum and D. microcarpum are proposed. Spore ornamentation of 95 specimens was studied with the scanning electron microscope. Diderma niveum var. ferrugineum is considered to be synonym of D. niveum. Two new combinations, D. niveum var. cristatosporum and D. alpinum f. microcarpum, are proposed and one new species, D. meyerae, is described.
Austria, Spain, Switzerland, France, new combinations, new species, Physarales, Diderma, SEM