The distinction of Laurencia truncata (Ceramiales, Rhodophyta) in the Mediterranean Sea from Laurencia pinnatifida

A study of Mediterranean specimens identified as Laurencia pinnatifida (Hudson) Lamouroux (Ceramiales, Rhodophyta) showed that they have to be referred to L. truncata Kützing. This species, occurring also in the Atlantic, where it was recorded under other names, shows the following main features: axes compressed; epidermal cells elongate, with secondary pit connections; medullary cells showing abundant lenticular thickenings; tetrasporangia, in parallel arrangement, cut off from the mother cells abaxially; antheridial branches unbranched, inserted in depressions that do not show a row of axial cells at their base. The species is included in the subgenus Laurencia, section Planae. The new subgenus Saitoa (type species L. pinnatifida), including the section Pinnatijidae J. Agardh emend. Furnari et Serio, is proposed. It is characterized by lack of secondary pit connections between epidermal cells and by parallel arrangement of tetrasporangia.