During an extensive survey of the terrestrial diatom flora of soils on Ile de la Possession (Crozet Archipelago, Subantarctica), three new species belonging to the diatom genus Diadesmis have been discovered: D. ingeae Van de Vijver sp. nov., D. vidalii Van de Vijver et Ledeganck sp. nov. and D. latestriata Van de Vijver, Ledeganck et Beyens sp. nov. The detailed morphology of the three new taxa has been examined in detail using Light (LM) and Scanning Electron Microscopy (SEM). Comparisons are made with similar Diadesmis species. Ecological data is provided for each species.