Abstract 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
cox 1) 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.