During a survey of the freshwater aquatic diatom flora of two peat bog areas in Tierra del Fuego, southern Argentina, a new taxon belonging to the genus Stauroneis that could not be identified was observed. Based on detailed light and scanning electron microscopy observations and comparison with similar larger-celled Stauroneis species worldwide, the taxon is described as new: Stauroneis fuegiana Casa & Van de Vijver sp. nov. Stauroneis fuegiana can be distinguished based on the slightly raised marginal crest, the typical broadly lanceolate valve outline with subrostrate apices, the almost rectangular central area and its valve dimensions.Comments are made on its taxonomic position and how the new taxon can be distinguished from other larger-celled Stauroneis species. Brief notes on the ecology and distribution are added.