Forty-eight soil samples were collected from Ile de la Possession, Crozet Archipelago. One hundred sixty-five taxa belonging to 32 genera were recorded. The cluster analysis revealed four assemblages, separated by a moisture and a possible pH-gradient. The Eunotia paludosa var. paludosa assemblage was found on relative wet acid soils, mostly bound to the valleys on the island. The less diverse Diadesmis contenta assemblage is typical for drier soils, occurring on the entire island. Two assemblages, i.e; the Fragilaria maillardii and the Achnanthes confusa assemblage, were found on wetter, non-acid soils. They are separated from each other by the degree of influence of salinity caused by animal transport and/or sea-spray with the F. maillardii assemblage occurring closer to the coastline and the penguin rookeries of the island.