A taxonomic review of the genus Hypnea (Gigartinales, Rhodophyta) in Brazil based on DNA barcode and morphology

The red algal genus Hypnea has a wide geographical distribution along the coast of Brazil, where it has economic and ecological importance. The relatively simple and plastic morphology, often influenced by the conditions of its habitat, complicates the identification of Hypnea species. In the past years, several studies dealing with the taxonomy of Hypnea on the coast of Brazil have changed considerably the known diversity of species in the region. Studies using molecular markers led to the description of new species, while other names were placed in synonymy. In this review, revaluation of the morphology and the addition of new sequences for COI-5P, UPA and rbc L-3P markers were used in order to better understand the diversity of Hypnea species and their range of distribution. An identification key is presented for eleven species of the genus Hypnea occurring on the coast of Brazil: H. brasiliensis P.B. Jesus, Nauer & J.M.C. Nunes, H. cervicornis J. Agardh, H. cornuta (Kützing) J. Agardh, H. cryptica P.B. Jesus & J.M.C. Nunes, H. edeniana Nauer, Cassano & M.C. Oliveira, H. flava Nauer, Cassano & M.C. Oliveira, H. pseudomusciformis Nauer, Cassano & M.C. Oliveira, H. platyclada P.B. Jesus & J.M.C. Nunes, H. spinella (C. Agardh) Kützing, H. yokoyana Nauer, Cassano & M.C. Oliveira and H. wynnei Nauer, Cassano & M.C. Oliveira. Of all taxonomic characteristics proposed by earlier studies, the only ones that have taxonomic value considering the species analyzed in this work were: (1) habit of the thallus, (2) main axis, (3) apex shape, (4) form of the branchlets and (5) tetrasporangial sori position in the branches. However, the identification of the species based only on morphological characteristics should be made with caution, once phenotypic plasticity and convergent morphologies are present in the group. The DNA barcode technique, especially the COI-5P marker, proved to be very effective in the identification and delimitation of the species, revealing scenarios that would go unnoticed by morphology alone.