Taxonomic re-examination of Japanese Halimeda species using genetic markers, and proposal of a new species Halimeda ryukyuensis (Bryopsidales, Chlorophyta)

In order to elucidate the biodiversity of Japanese Halimeda species, we investigated molecular phylogenetic relationships using tufA and rbcL DNA sequences, and the occurrence of 9 of the 11 species previously reported in Japan was confirmed (i.e., H.borneensis, H.cuneata, H.discoidea, H.distorta, H.kanaloana, H.macroloba, H.opuntia, H.renschii and H.velasquezii). In addition, H.minima, which has not been recorded in Japan, as well as an undescribed taxon, were noticed at Okinawa Island, Okinawa, Japan. The undescribed taxon was genetically closest to H.lacunalis, but distinct from that species in having much smaller thalli, with elliptical segments and turbinate peripheral utricles. It appears to belong to the section Halimeda in the morphology of the segments, but differs from related taxa such as H.taenicola and H.tuna in its considerably smaller size and in showing fusion between the adjacent peripheral utricles. Therefore, we describe a new species Halimeda ryukyuensis sp. nov. In addition, based on morphological re-examination of the type specimen of H.lacunalis, we suggest emendation of the description of the species as having siphons completely fused in pairs or triplets at the nodes.