Confirmation of the status of three Pterocladia species (Gelidiales, Rhodophyta) described by K. Okamura

Abstract

We determined nucleotide sequences of the plastid-encoded large subunit of the ribulose-1,5-bisphosphate carboxylase/oxygenase gene of 21 populations of the Pterocladia/Pterocladiella-complex in Japan. Three monophyletic clades were recognized. These include one group that comprised the most southern population, a second group that contained four populations from western to central Japan (98% bootstrap value), and a third group that consisted of the rest of populations examined and Pterocladiella capillacea (S. Gmelin) Santelices et Hommersand, from Australia, Spain, and Italy (82% bootstrap value). We have also demonstrated that these three groups can be recognized by the discontinuity of morphological measures, including the length of the axes and first-order branches, width of the second-order branches, and branching intervals of axes and first-order branches. The morphological distinctiveness of these three groups was maintained under uniform culture conditions. The molecular and morphological data indicate that these three groups represent distinct species. On morphological grounds, group 1 can be assigned to Pterocladia nana Okamura, group 2 to Pterocladia tenuis Okamura, and group 3 to Pterocladia densa Okamura. Although P. densa is a synonym of P. capillacea, P. nana and P. tenuis are transferred to Plerocladiella owing to the production of Pterocladiella-type cystocarps. The following new combinations are therefore proposed: P. nana (Okamura) Shimada, Horiguchi et Masuda and P. tenuis (Okamura) Shimada, Horiguchi et Masuda. Gelidium decumbensum Okamura is reduced to a synonym of P. tenuis.