Devaleraea titlyanova sp. nov. (Palmariaceae, Rhodophyta) from the Russian coast of the northwestern Pacific Ocean

One species of the red algal genus Devaleraea, D. stenogona, shows remarkable phenotypic plasticity over its geographic range. We assumed this species to be a complex of morphologically close species. To resolve this issue, we sequenced the internal transcribed spacer (ITS) regions, including the 5.8S rDNA, rbcL, and 5 ' end of the COI gene (COI-5 ') of specimens of D. stenogona sensu lato from different localities along the Russian coast of the northwestern Pacific Ocean. We also compared their morphology with the holotype and to specimens of D. stenogona from the type locality. Morphological and genetic analyses confirmed that Devaleraea stenogona sensu lato is a complex of two congeneric species and, therefore, the new species D. titlyanova sp. nov. is proposed. This species is characterised by abundantly proliferating thalli, with proliferations being larger than the main blade. First-year non-proliferating plants can be confused with D. stenogona, but they differ by a more regular dichotomous branching and by the shape of terminal branches, which are strap-shaped with rounded tips in D. titlyanova and narrow-linear or hair-like with acute tips in D. stenogona. The species have different geographical distributions with D. stenogona occurring further south than D. titlyanova.