No abstract

The filamentous red algal genus Gayliella, typified by G. flaccida, was segregated from Ceramium for a group of epiphytic species on the basis of morphological data and molecular phylogenetic analyses. However, while the genus was well investigated in some geographical areas, the treatment of the Brazilian taxa “Ceramium flaccidum” and “C. dawsonii” was incomplete and they were not transferred to Gayliella due to the problematic status of the specific epithets. Brazilian “C. flaccidum” did not fit within the circumscription of Gayliella flaccida; Brazilian “C. dawsonii” was positioned in three distinct lineages, none of which corresponded to known Gayliella species. Since the establishment of Gayliella, there has been no re‐evaluation of Brazilian species, so this study revises the genus in Brazil using molecular and morphological data. Brazilian “C. flaccidum”, “C. dawsonii”, and other Brazilian collections were investigated by an integrative approach using phylogenetic analysis, genetic divergence, two species delimitation methods using three molecular markers (rbcL, cox1, and partial LSU), and comparative morphological and quantitative analyses. This molecular‐assisted alpha taxonomy (MAAT) analysis placed Brazilian samples in five distinct well‐supported lineages. For these, we propose a new combination, Gayliella dawsonii comb. nov. (lineage 2), based on analysis of type specimens and molecular data obtained from specimens collected near the type locality, and four new species: Gayliella ardissonei sp. nov. (“Ceramium flaccidum” from Brazil), G. iemanja sp. nov. (“C. dawsonii” lineage 3), G. tamoiensis sp. nov., and G. jolyana sp. nov. (“C. dawsonii” lineage 1).

The cosmopolitan genus Ceramium (Ceramiaceae, Rhodophyta) is a large and systematically complex group. The taxonomy of this genus remains in a chaotic state due to the high degree of morphological variation. Culture studies, suggesting a strong influence of environment on phenotype, and the use of molecular tools have recently questioned the validity of morphological features used in species recognition. Here we compare three Ceramium taxa from Venice lagoon with samples from northwest Europe using the plastid ribulose–1,5–bisphosphate carboxylase/oxygenase gene (rbcL) and the rbcL–rbcS intergenic spacer combined with morphological observations. A strongly banded species, previously identified as member of a poorly understood and misnamed group, the Ceramium diaphanum complex sensu Feldmann–Mazoyer, is probably conspecific with British samples of Ceramium diaphanum sensu Harvey, for which no valid name has been identified up to now. We show that Ceramium polyceras (Kützing) Zanardini is a valid name for this species. A fully corticated Ceramium species morphologically resembling C. secundatum differs at the species level from Atlantic C. secundatum; a valid name for this entity is Ceramium derbesii Solier ex Kützing, described from Mediterranean France. A third species characterized by cortical spines, previously listed as Ceramium ciliatum var. robustum (J. Agardh) Mazoyer, is shown to be Ceramium nudiusculum (Kützing) Rabenhorst, originally described from Venice.