Molecular characterization of the genus Ceramium (Ceramiaceae, Rhodophyta) in the transitional environments of the Venice Lagoon

The cosmopolitan genus Ceramium Roth (Ceramiaceae, Rhodophyta) is one of the largest and most systematically complex Rhodophyta group. Taxonomical problems are mainly tied to the unusually highly variable morphology observed inside the genus. In spite of this, Ceramium species inventory in many areas is based only on morphological observations and several classification problems are still opened. One of these areas is the Venice Lagoon, where we have recently sampled several Ceramium specimens. Through accurate morphological observations and phylogenetic analyses, based on the plastid ribulose-1,5-bisphosphate carboxylase/oxygenase gene (rbcL) and the RuBisCo intergenic spacer (rbcL-rbcS spacer) as molecular markers, we identify three distinct Ceramium taxonomic entities, two of which never reported before in this environment according to the available checklists based only on morphology. The validity of the three entities as recognizable species is also discussed.