Gracilaria suzannae sp. nov. (Gracilariales, Rhodophyta), a new flattened species from northeast Brazil based on morphological and molecular evidence

A new species of Gracilaria, G. suzannae sp. nov., is described on the basis of detailed morphological, anatomical and molecular evidence from recent collections from intertidal reefs of northeastern Brazil. Diagnostic features of the new species include: tufted and tough thalli with subdichotomous, alternate to irregular branches; some branches incurved, with discrete marginal teeth, giving thalli a dentate to lacerate appearance in the upper parts; an abrupt transition of cell size between cortical and medullary regions; spermatangial conceptacles of the textorii type; and mature cystocarps with inconspicuous inner pericarp and few tubular nutritive filaments, particularly in basal portions. Universal plastid amplicon sequences of G. suzannae formed a distinct group within the genus Gracilaria, with intraspecific divergence of 0.24%. In the rbcL analysis, G. suzannae was recovered as sister to a well-supported Glade containing G. occidentalis from the United States, with interspecific divergence of 1.3%. Unlike our specimens, the thallus habit of G. occidentalis is repeatedly forked, with smooth margins and rounded apices. Furthermore, G. suzannae was phylogenetically positioned close to a major Glade composed of Indo-Pacific flat species with lobed, spiny or denticulate margins, all of which diverged 1.1 to 4.8% from G. suzannae. Gracilaria suzannae becomes the 16th flat species of Gracilaria reported for Brazil.