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Recent taxonomic studies of the genus Laurencia sensu lato (Ceramiales, Rhodomelaceae) have resulted in the recognition of three genera within the ‘Laurencia complex’: Laurencia sensu stricto, Chondrophycus and Osmundea. A critical examination of all Mediterranean records of taxa referred to Laurencia has shown that three species of Chondrophycus, six species of Osmundea and nine species of Laurencia are present. These taxa are described and illustrated. Laurencia caduciramulosa and L. intricata are reported for the first time from the Mediterranean Sea and from Italy, respectively. A key to the Mediterranean species of the Laurencia complex is given.

A study of the morphology of the brown alga Cystoseira susanensis , a species known only from the type locality (Susa, Lybia) and from southeastern Sicily, was carried out on numerous thalli occurring in littoral rockpools at Marzamemi (Syracuse, Italy). The species has a short primary axis bearing numerous secondary axes close to the base. Such a branching pattern probably led Nizamuddin to consider his species as caespitose, while, on the contrary, it is not caespitose. Observations in culture of the first phases of segmentation of zygotes as well as of the first growth stages of germlings are also provided.

The original collections of Cystoseira algeriensis J. Feldmann and of Cystoseira elegans Sauvageau, both held in the Herbarium of the Laboratoire de Cryptogamie, Museum National d'Histoire Naturelle (PC), were examined and lectotypes were designated, since no holotypes were indicated by original authors.