Rhodachlya westii sp. nov. (Rhodachlyales, Rhodophyta), a new species from Brazil, revealed by an integrative taxonomic approach

A small red alga was isolated into culture from rhodoliths collected on the Piaui coast, northeastern Brazil. Molecular data from the plastid-encodedrbcL gene, combined with morphological and ultrastructural evidence, demonstrated that it belongs to the genusRhodachlyaand supports the proposal of a new species,R. westii. The new species was characterised by basal and erect uniseriate filaments, cells with parietal H-shaped or lobed plastids with one or two prominent pyrenoids, absence of unicellular hairs, and with monosporangia sessile or on branched stalks. Ultrastructure revealed pit plugs with two cap layers without a cap membrane, typical of Rhodachlyales. In ourrbcL phylogeny,R. westii sp. nov. was recovered in a well-supported clade containingR. hawaiianaandR. madagascarensis(generitype) with interspecific divergence ranging from 5% to 10%, respectively. Characters previously used for species-level taxonomy (e.g. cell dimensions, number of pyrenoids and presence or absence of colourless hairs) are often plastic and overlap. We conclude thatRhodachlyaspecies can be accurately identified only based on DNA sequence data and their geographic distribution.Rhodachlya westiibecomes the third species of the genus, representing the first record in the Atlantic Ocean. Our data suggest that the genus is probably widely distributed. In view of the scarcity of reliable morphological features available for comparison, molecular-assisted alpha taxonomy is needed for uncovering the long-overlooked diversity in this red algal group.