Brown algae of the genus Cystoseira sensu lato form the most diverse and productive marine ecosystems throughout the Mediterranean Sea and have equal roles also in the Black Sea where they have been decreasing in the recent years. The taxonomy of Cystoseira s.l. taxa from the Black Sea is still not well understood, and questions arise when related taxa have to be delimited. In addition to morphological descriptions, this study provides for the first time molecular data of the Black Sea Cystoseira s.l. distinct morphologies as an additional tool to clarify their identities and phylogenetic affinities. The analysis of two mitochondrial markers (cytochrome oxidase subunit 1—COI, and 23S-tRNAVal intergenic spacer—mt-spacer) showed that Cystoseira s.l. specimens from the Black Sea belong to two recently resurrected genera, namely Gongolaria and Ericaria. Molecular data confirm the morphological identification of G. barbata, which is characterized by high morphological plasticity in the Black Sea. The morphological data presented in this study support the transition of G. barbata to the genus Gongolaria, which was previously proposed based solely on genetic data. For the Black Sea endemic taxon C. bosphorica, sequence divergence suggests conspecificity with Mediterranean Sea species E. crinita and E. barbatula. However, considering original morphological characteristics of the taxon, its geographical isolation, and endemism, the new combination Ericaria crinita f. bosphorica comb. nov. is proposed.

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Cystoseira sensu lato (Ochrophyta) forests are important habitat formers in the Mediterranean Sea, but they have mostly been studied in the western basin where many species are under decline. In the eastern basin, where fewer species occur, Cystoseira rayssiae Ramon was described in the year 2000 as an endemic species based on morphological characteristics from herbaria samples collected on the Israeli coast. No further investigations have been conducted on this peculiar species since, but recently it has been recorded in contiguous Lebanon and outside the Mediterranean. Our work was aimed at confi rming the taxonomic validity and endemic nature of this species, including its position among the recently split Cystoseira sensu stricto, Carpodesmia Greville and Treptacantha Kützing genera, by sequencing the mitochondrial COI gene and by examining morphological characteristics in samples from three diff erent sites in northern Israel. Notwithstanding considerable morphological plasticity, molecular analyses revealed a single unique COI sequence. Phylogenetic analyses show that Cystoseira rayssiae belongs to the resurrected genus Treptacantha and hence, the new combination Treptacantha rayssiae (Ramon) M.Mulas, J.Neiva & Á.Israel, comb. nov., is proposed. Unique sequences and a restricted range support its Levantine-endemic status. Intriguing extra-Mediterranean reports from the Red Sea and the Persian Gulf are probably misidentifi cations rather than refl ecting a disjunct distribution or recent invasion. RÉSUMÉAffi nités génétiques et biogéographie du peigne d'algues marines Levantine-endémique Treptacantha rayssiae (Ramon) M.Mulas, J.Neiva et Á.Israel, comb. nov. (Phaeophyceae). Les forêts de Cystoseira sensu lato (Ochrophyta) sont d'importantes formes d'habitat dans la mer Méditerranée, mais elles ont surtout été étudiées dans le bassin occidental où de nombreuses espèces sont en déclin. Dans le bassin oriental, où moins d'espèces sont présentes, Cystoseira rayssiae Ramon a été décrite en l'an 2000 comme une espèce endémique sur la base des caractéristiques morphologiques d'échantillons d'herbiers prélevés sur la côte israélienne. Aucune autre enquête n'a été menée sur cette espèce particulière depuis, mais récemment, elle a été enregistrée dans le Liban contigu et en dehors de la Méditerranée. Notre travail visait à confi rmer la validité taxonomique et la nature endémique de cette espèce, y compris sa position parmi les genres Cystoseira sensu stricto, Carpodesmia Greville et Treptacantha Kützing récemment divisés, en séquençant le gène mitochondrial COI et en examinant les caractéristiques morphologiques dans des échantillons provenant de trois sites diff érents dans le nord d'Israël. Malgré une plasticité morpho logique considérable, les analyses moléculaires ont révélé une seule et unique séquence COI. Les analyses phylogénétiques montrent que Cystoseira rayssiae appartient au genre ressuscité Treptacantha et, par conséquent, la nouvelle combinaison Treptacantha rayssiae (Ramon) M.Mulas, J.Neiva & Á.Israel, ...

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