Kapraunia silviae (Rhodomelaceae, Rhodophyta), a new species from the South Atlantic Ocean

Kapraunia is a genus recently segregated from Polysiphonia sensu lato, with only four species so far known. However, no species have been found on the South Atlantic coast. Recent collections in southwestern Brazil revealed specimens morphologically similar to Kapraunia spp. To investigate the identity of these specimens, we carried out a morphological and molecular study based on COI-5P and rbcL sequences. Phylogenetic analysis placed our samples within the genus Kapraunia as a new species with full support, described here as Kapraunia silviae sp. nov. K. silviae is recognizable by a combination of characters such as attachment by a basal disc and a prostrate system, branches developing laterally to the trichoblasts, 5–6 pericentral cells, rarely 4. The species differs from K. pentamera by the attachment form, segment proportions and tetrasporangial dimensions, and from K. schneideri by the number of pericentral cells, branch development and tetrasporangial arrangement. Re-examination of herbarium samples from Brazil in older collections also revealed misidentifications of K. silviae as “Carradoriella denudata”. This new species seems to be restricted to the Brazilian coast, being found only on the northern coast of São Paulo state. Our results reinforce the need for revision of Polysiphonia s.l. species on the Brazilian coast.