Diversity of Cystoseira sensu lato (Fucales, Phaeophyceae) in the eastern Atlantic and Mediterranean based on morphological and DNA evidence, including Carpodesmia gen. emend. and Treptacantha gen. emend.

The diversity and phylogenetic relationships of specimens in the brown algal genus Cystoseira sensu lato from the eastern Atlantic and Mediterranean were examined using DNA sequences for four genetic markers (psbA, mt23S, cox1 and nad1). Our results provide evidence to resolve most of the species documented in the eastern Atlantic and Mediterranean as Cystoseira in three clades that are interpreted here as representing three genera. Morphological studies confirmed the distinctness of the genera and identified characters that distinguish species. One clade corresponds to Cystoseira sensu stricto, including the type species C. foeniculacea, together with C. compressa, C. humilis and the resurrected species C. aurantia. Species in Cystoseira are characterized by a caespitose habit and receptacles with grouped conceptacles lacking spiny appendages. The second clade corresponds to Treptacantha gen. emend., with T. abies-marina as the type species. A further 11 Atlantic and/or Mediterranean species were transferred to this genus. The concept of Treptacantha was better redefined, using the following morphological characters: smooth primary branches at least in the basal region, cortical cells with thickened walls and square meristoderm cells in cross section. The third clade corresponds to Carpodesmia gen. emend., with C. zosteroides as the type species. Another six Mediterranean species and the Atlantic/Mediterranean C. tamariscifolia were transferred to this genus. The concept of Carpodesmia was better defined to include new morphological features: all branches having spines, cortical cells with thin walls and rectangular meristoderm cells in cross section.