Systematic revision of the Grateloupia complex (Rhodophyta) from Vietnam using rbcL and LSU sequences, with the description of Phyllymenia nhatrangensis sp. nov.

Grateloupia sensu lato has had a long and troublesome taxonomic history because of superficial similarities in morphology, ill-defined species boundaries and lack of diagnostic characters that leave many gaps that still need to be fully resolved. In this study, we carried out detailed observations on female reproductive structures, and inferred the phylogenetic relationships of the Grateloupia-like species occurring in Vietnam based on rbcL and LSU rDNA sequence analyses. The new species Phyllymenia nhatrangensis sp. nov. differs from its sister species P. gibbesii in the thickness of the cortex. The new species is slightly flattened, composed of two to four main blades, bearing numerous marginal and a few superficial, lanceolate bladelets. Blade sizes of P. nhatrangensis are also smaller than those of P. gibbesii, which are longer and wider. However, the new species shares with species from western Pacific Ocean, such as P. taiwanensis and P. huangiae, the presence of frequent marginal proliferations. Based on rbcL, the divergence between P. nhatrangensis and P. gibbesii was 3.3% (39 bp). With the present addition, Grateloupia sensu lato now comprises 16 species, including nine species of Grateloupia, three species of Phyllymenia, two species of Yonagunia and one species each of Dermocorynus and Prionitis.