On the occurrence of Mesophyllum expansum (Philippi) Cabioch et Mendoza (Melobesioideae, Corallinales, Rhodophyta) in the Mediterranean Sea, the Canary Isles and the Azores

We reviewed literature records, examined herbarium specimens and studied new collections referred to as Mesophyllum lichenoides from the Mediterranean and the North Atlantic, and report for the first time the presence of Mesophyllum expansum in the Canaries and the Azores. Both gametophytes and tetrasporophytes of M. expansum occur in the Canaries, while we found only tetrasporophytes (and sterile thalli) of the species in all other regions. We further consider the presence of M. lichenoides further south than Atlantic France in need of confirmation. A comparative study between these two species points to the number of rosette cells as the most reliable and easily diagnosed character, M. expansum most often having 9-11 and M. lichenoides 6-8 cells.