Updating of Ceramium (Rhodophyta, Ceramiales) biodiversity in the North Adriatic Sea (Mediterranean) based on a molecular and morphological approach. Ceramium systematics North Adriatic Sea

The cosmopolitan genus Ceramium Roth (Ceramiaceae), with about 211 currently accepted species, is one of the largest in the Rhodophyta. This genus is characterized by cylindrical or slightly compressed thalli, whose axial cells are incompletely to completely covered by cortical cells, with alternate to pseudo-dichotomous branching, and straight to inrolled apices. It typically occurs in eulittoral or shallow subtidal habitats and its worldwide distribution is often connected with naval traffic. The nomenclature and taxonomy of this genus are still in a state of chaos. Taxonomic problems are linked to the high degree of variation in the morphological characters classically used for species recognition. At the same time, the identification of new species is often complicated by their small sizes, epiphytic habit, and by the presence of cryptic taxa. The strong influence of environment on morphology, highlighted also by the use of molecular tools, has questioned the validity of certain morphological features to discriminate different Ceramium species.In this study we characterize different Ceramium isolates sampled in transitional waters of the Venice Lagoon (Italy) by a molecular and morphological point of view. Through phylogenetic analyses, using partial sequences of the plastid ribulose-1,5-bisphosphate carboxylase/oxygenase gene (rbcL) as molecular marker, we identify six distinct taxonomic entities, of which four represents new taxa never reported before in the Venice Lagoon.