Mesotaenium berggrenii belongs to the few algae that have adapted to live on bare glacial surfaces. Although it is regarded as a cosmopolitan in alpine and polar regions, reports of occurrence are quite sparse. This is probably because of the inconspicuousness of their growing sites, where even mass accumulations only cause a greyish colouration of the white substrate. We characterise a community in the European Alps, including ecophysiological habitat parameters. The field samples consist of two size classes; the smaller one was recognised as M. berggrenii var. alaskana, which contains only one chloroplast per cell after cell division instead of two. This is the first report on the rediscovery of this variety since its description in 1942 and also the first work on its ultrastructure. The results show that M. berggrenii is able to persist in its harsh habitat without formation of cysts, which is in contrast to many snow algal species. The vegetative cells of this cold-adapted species contain high amounts of intraplastidal starch, cytoplasmic lipid bodies as well as many peripheral vacuoles. Organelles, like the Golgi stacks or chloroplasts, are well developed and do not show any signs of morphological reduction, as in cysts. The ecological function of a brownish secondary pigment, a putative polyphenol occurring in high concentrations in vacuoles, is discussed. Screenings by high-performance liquid chromatography reveal the presence of primary photosynthetic pigments characteristic for green algae, but no flavonoid-like phenolic compounds are found.