Boreolithothamnion acuminatum sp. nov., B. homoglobosum sp. nov., B. jejuensis sp. nov., and B. japonium comb. nov. (Hapalidiales, Rhodophyta) from Korea: Expanding diversity and biogeographic range in the Northwest Pacific region.

The non-geniculate coralline genus Boreolithothamnion currently includes eight species with a Northern Hemisphere distribution. To date, only a few studies have focused on the systematics of Boreolithothamnion species. Here, we performed morphological and phylogenetic analyses, based on rbcL, psbA, and SSU rRNA gene datasets, on Boreolithothamnion from Korea as well as DNA-sequenced type material representing nine names. The analyses supported the proposal of three new species of Boreolithothamnion from Korea: B. acuminatum sp. nov., B. homoglobosum sp. nov., and B. jejuensis sp. nov. Boreolithothamnion acuminatum is distinguished by its encrusting to warty growth form, acuminate to cylindrical protuberances, and raised to low-domed tetra/bisporangial conceptacles having bordered pore canals with three to four roof cells. Boreolithothamnion homoglobosum is characterized by a fruticose or unattached rhodolith and simple to bifurcated protuberances. Boreolithothamnion jejuensis is distinguished by an encrusting to undulate or knobby growth form with unbranched protuberances. Phylogenetic analysis of the holotype of Lithothamnion japonicum (TRH C16-3267) based on the psbA gene strongly supported its transfer to the genus Boreolithothamnion, B. japonicum comb. nov. Eight other type specimens of Lithothamnion were also observed to cluster within the Boreolithothamnion clade and were resolved with previously accepted species. This study expands the biogeographical range of Boreolithothamnion in the Northwest Pacific.