Article

The red algae (Rhodophyta) currently comprise some 828 genera and over 4500 species of which some 200 genera and over $50 species are recorded in the Mediterranean region. Molecular data along with ultrastructural characteristics support the subdivision of red algac in the Bangiophyceae and the Florideophyceae, the latter group distinguished mainly by having cap membranes covering pit-plugs and specialised gametangia (spermatangia and carpogonia the latter provided with trichogynes). The Florideophyceae are subdivided in two main lineages: the first includes the Acrochactiales, Palmariales, Nemaliales, Corallinales. Barrachaspermales and the Rhodogorgonales, which are distinguished by having outer cap lay- ers covering their pit-plugs: the second lineage is distinguished by the loss of inner cap layers and includes the Gigantinales. Cryptonemiales. Rhodvmeniales. Gracilariales, Bonnemaisoniales, Gelidiales, Ceramiales, and the Ahnfeltiales. Multicellular carpogonial branches, auxiliary cells, ooblasts, axial or lateral carpogonial branches, and procarpic or non- procarpic conditions have independently developed in both lineages and apparently represent non-homologous structures at this level of phylogenetic resolution. Relationships at infra-ordi- nal level remain largely speculative and it is here where the above mentioned morphological characters will contribute in the systematics. The Mediterranean marine flora has undergone profound changes since the basin was created in the Palacozoic and presently has many taxa in common with the neighboring Atlantic, while it has received several alien species in the past 100 years. Most significantly, it includes palacoendemics and neoendemics and clarifying the systematic position and origin of these unique elements can help us understand the evolution of red algae in general.