The genus Hydrolithon, together with Porolithon, is one of the most discussed groups of Corallinaceae, as well as one of the most poorly known. Morphological observations led to different interpretations mainly due to the lack of type material. Recently molecular surveys on the phylogeny of Corallinales supported the hypothesis of considering Hydrolithon and Porolithon as two distinct genera, but, up to now, several taxonomic questions remain partially unanswered. In this study we report the discovery of a new non-geniculate encrusting species found along the coast of Vis Island, Croatia, Adriatic Sea. Morphological observations suggest that the specimens could belong to the Hydrolithon/Porolithon complex. Molecular analyses based on the nuclear 18S rDNA (SSU) and the plastidial psbA markers were carried out. This finding represents the first report of this new coralline alga in the Mediterranean Sea.
