A comparative study between Lithothamnion minervae and the type material of Millepora fasciculata (Corallinales, Rhodophyta)

Lithothamnion minervae is a crustose coralline alga recognized as a common rhodolith-forming species in the western Mediterranean basin. The species was erected in order to give a correct name and an unequivocal definition to the coralline misidentified for a long time as Lithothamnion fruticulosum. Details of the plant, such as the epithallial cells and the tetrasporangial or bisporangial and uniporate conceptacles are described on recently collected samples. It is shown that the two plants in the original collection of Millepora fasciculata belong to different taxa, and therefore a previous lectotypification (Woelkerling in Woelkerling & Lamy 1998) is superseded. The smaller of the two plants, which belongs to an undescribed species of Clathromorphum, is selected here as the new lectotype of M. fasciculata. The larger plant in the collection belongs to a species of Lithothamnion; it differs from L. minervae in having a smaller range of chamber diameters of multiporate conceptacles. embedded multiporate conceptacles filled with palisade cells and smaller perithallial cells.