Extension of the distribution range of Hypnea stellulifera (Cystocloniaceae, Rhodophyta) to the South Atlantic: Morphological and molecular evidence

•Hypnea stellulifera is reported for the first time in the Atlantic Ocean.•The markers cox1, rbcL and UPA were efficient in identifying taxonomic groups in Hypnea.•Expansion of geographical sampling shows unexpected levels of intraspecific variation in Hypnea.•Previous phylogeny of species of Hypnea determined morphologically is not supported by the molecular data.

Hypnea stellulifera was, until now, considered endemic to tropical Asia. Here, we report for the first time the expansion of its distribution to the Atlantic Ocean on the basis of collections from the northeast of Brazil. Comparison of morphological features of our specimens with Asian specimens of H. stellulifera and molecular data analysis allow us to confirm its identification. Samples analyzed in this study represent the first assessment of Hypnea sequences collected in a tropical area from South America. Among the three genes analyzed (the mitochondrial cox1 and the plastidial UPA and rbcL), UPA was the most conserved, and the cox1 was the most variable marker. Despite this, all three markers were efficient as DNA barcoding markers for Hypnea. In our phylogenetic analysis, H. stellulifera had a sister relationship with the clade that includes H. cornuta, H. musciformis, H. flagelliformis, and H. chordacea. Our results demonstrate that the analysis of Hypnea species collected at large geographic distances and/or in different tropical areas reveals a higher degree of intraspecific variation as well as decreased interspecific divergence among distinct species from closer areas. These findings corroborate the necessity of a combined analysis of morphology and different genetic markers for a better understanding of taxonomy and phylogeny of the genus Hypnea.