A survey of the species of Cystoseira (Fucales, Phaeophyceae, Ochrophyta) of Tunisia highlighted six Mediterranean endemic taxa rare or new for this country: C. barbata f. aurantia, C. brachycarpa var. claudiae, C. compressa subsp. pustulata, C. foeniculacea f. dubia, C. hyblaea and C. spinosa var. tenuior. The discovery and the study of these species, some of which were little known, have allowed some taxonomic and biogeographical uncertainties to be identified and discussed. On the basis of the results, the transfer of C. discors f. dubia to C. foeniculacea as C. foeniculacea f. dubia and the reinstatement of species rank for the Mediterranean endemic species C. schiffneri are proposed.