Taxonomy and distribution of selected species of the agarophyte genus Gelidium (Gelidiales, Rhodophyta)

Although the diverse uses of Gelidium as food and in the production of agar and paper pulp have increased research interest in this genus, the taxonomy and biogeography of several species of Gelidium remain largely unstudied. We conducted phylogenetic analyses of mitochondrial cox1 and plastid rbcL sequences of selected species of Gelidium. The data revealed that Gelidium allanii, Gelidium johnstonii, and Gelidium koshikianum, species that share a similar morphology, formed a monophyletic clade with a wide distribution around the Pacific rim. Because G. johnstonii Setchell & Gardner has nomenclatural priority over G. allanii V.J. Chapman and G. koshikianum Shimada et al., we synonymize the latter two species with the former. Based on the extremely low genetic divergences (0.0-0.2 % for rbcL and 0.0-0.4 % for cox1) between Korean and Mexican specimens of G. johnstonii and its sister relationship with Asian species, we consider that G. johnstonii may have been recently dispersed by anthropogenic agents. The New Zealand endemic Gelidium longipes and Gelidium crinale from Australia were compared with both rbcL and cox1, and were found to be identical. Although the transfer of G. logipes to G. crinale is necessary, the Australasian group within G. crinale is separated from other populations of the species, and we therefore recognize it as a subspecies. Biogeography of Gelidium on the basis of rbcL phylogeny of the 59 Gelidium species is briefly discussed.