During a survey of the freshwater and terrestrial diatom flora of the Crozet and Kerguelen archipelagos, two new species, Geissleria taafiana and Geissleria subantarctica, belonging to the genus Geissleria Lange-Bertalot & Metzeltin were recorded. The detailed morphologies of the two species are examined using light (LM) and scanning electron microscopy (SEM). The new species are compared with similar Geissleria species. © 2003 J. Cramer in der Gebrüder Borntraeger Verlagsbuchhandlung.