To be or not to be Aeodes? That's the matter of A. marginata (Halymeniaceae, Rhodophyta).

In 1876, J. Agardh described the new genus Aeodes with a single species, A. nitidissima, from New Zealand. Later, Schmitz in 1894 added a new species, A. ulvoidea, from South Africa andtransferred to this genus Schizymenia marginata (Roussel) J. Agardh from the Mediterranean, and Iridaea orbitosa Suhr from South Africa. Both in the present study and in literature, the molecular phylogenetic trees show that Pachymenia J. Agardh 1876 is the sister genus of Aeodes and their species form a well supported clade. Also Pachymenia species are presently distributed in the southern hemisphere. Aeodes marginata (Roussel) F. Schmitz is an exception, being endemic of the Mediterranean. In the present study, A. marginata is included in a large and not completely resolved clade together with Halymenia species, Cryptonemia species, Carpopeltis phyllophora, and Acrodiscus vidovichii. Anatomically, A. marginata differs from Aeodes/Pachymenia species by the presence in its medulla of refractive stellate cells and of anticlinal pluricellular filaments connecting periclinal pluricellular filaments. Furthermore, the shape of auxiliary ampulla and the germination of the spores of A. marginata are reported to be of the Halymenia type and not of the Aeodes type. Therefore, both vegetative and reproductive structures prove the affinity of A. marginata with the above-mentioned genera; nevertheless it presents its own unique set of characters. All the evidences suggest that A. marginata does not fit in its present genus and need a new taxonomical position in the Halymeniaceae.