Taxonomy and phylogeny of flattened species of Gracilaria (Gracilariceae, Rhodophyta) from Korea based on morphology and protein-coding plastid rbcL and psbA sequences

Despite extensive studies on cylindrical Gracilaria species, the taxonomy and phylogeny of the flattened species of the genus has received little attention. We studied the morphology and molecular phylogeny of three flattened species of Gracilaria, hitherto reported from Korea. Gracilaria textorii is characterized by having a wider blade relative to other species, margins entire or proliferous, coriaceous thallus texture, one to three large cells in the medulla, and shallow male conceptacles. Gracilaria cuneifolia is membranous in texture, and has shallow spermatangial conceptacles (approximately 10 mu m in depth). We generated psbA and rbcL sequences from 32 specimens of G. textorii, G. cuneifolia and its putative relatives in Korea and surrounding waters. Twenty-three specimens of G. textorii from Korea, including two from Japan, were almost identical in both rbcL and psbA regions, except for some specimens that were different by one to four nucleotides. Three specimens of G. cuneifolia were identical in both rbcL and psbA. However, we found no evidence for the occurrence of G. incurvata in Korea. In all analyses of rbcL, psbA, and rbcL + psbA data sets, G. textorii was determined to be a unique species, with G. incurvata from Japan as a sister species. Gracilaria cuneifolia is more closely related to the G. tikvahiae group from the Atlantic than G. textorii and G. incurvata.