Boreolithothamnion astragaloi, a coralline algal species belonging to the family Hapalidiaceae and order Hapalidiales, has been reported from British Columbia, Canada in northeastern Pacific. In this study, we report B. astragaloi for the first time from Korea, representing its initial record in the northwestern Pacific. Morpho-anatomical and molecular analyses of Lithothamnion-like specimens collected in Korea revealed that some individuals correspond to B. astragaloi. This species is characterized by flattened, flared epithallial cells; subepithallial initials as long as or longer than the cells immediately subtending them; cell fusions; multiporate tetrasporangial conceptacles; and tetra/bisporangial conceptacles developed from small groups of subepithallial initials. Phylogenetic analyses based on the COI-5P, psbA, and rbcL datasets place B. astragaloi firmly within the Boreolithothamnion clade, supporting its identification and extending the known distribution of the species to the northwestern Pacific.

Roseolithon sabulosum, a coralline algal species within Hapalidiaceae, has been documented from Japan. Phylogenetic analyses based on rbcL and psbA sequences confirmed that the Korean non-geniculate coralline algal specimens from Jeju Island are conspecific with Japanese R. sabulosum, including the holotype. Additionally, both morpho-anatomical and molecular analyses confirmed the identity of our specimens as R. sabulosum. Roseolithon sabulosum is characterized by flared epithallial cells, variable subepithallial initials, and multiporate tetra/bisporangial conceptacles elevated above the thallus surface with 4-7 rosette cells in conspicuous depressions that produce a pitted appearance. Its conceptacle roofs are composed of 3-6 cell layers, and pore canals are lined by 2-4-celled filaments containing rosette cells with disintegrated roofs underlain by elongate to wedge-shaped cells longer than other roof cells. In this study, we report R. sabulosum for the first time in Korea, thereby broadening its known distribution to include both Korea and Japan.