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.

A crustose red alga, Lithophyllum neo-okamurae A.Kato, D.Basso, Caragnano, Rodondi, V.Peña & M.Baba, is reported a new record from Korea and its biogeographic distributions are extended in Korea. Lithophyllum neo-okamurae has been known as endemic species in Japan. Despite the resemblance between L. neookamurae and L. okamurae, our molecular and morphological analyses have revealed the simultaneous presence of both species in Korea. Although L. neo-okamurae and L. okamurae share morphological similarities, there are notable variations in gene sequences, with a range of 9.1-11.3% in psbA and 14.8-15.3% in rbcL. Specifically, while L. neo-okamurae is distributed throughout the entire coastline of Korea, L. okamurae is predominantly found in southern region. Furthermore, our analyses have revealed their detailed distributions in Korea.

Pseudolithoderma subextensum is a crustose brown algal species in the family Lithodermataceae and order Sphacelariales. This species is distributed in several regions across the world including, Europe, Western Atlantic, Middle East and Asia (Hong Kong and Japan). Recent floristic surveys along the Korean coastal shores have revealed new records of encrusting brown algae. In this study, we report P. subextensum as a new record from Korea. Morpho-anatomical and molecular studies on Ralfsia-like specimens from Korea identified some of them as P. subextensum. Pseudolithoderma subextensum is characterized by dark chestnut brown crust with a hypothallial basal layer and erect perithallial filaments, tufts of hairs occasionally arising from the basal layer, several discoid shaped chloroplasts per cell, plurangia arising terminally on erect filaments and without sterile cells, and unangia arising terminally on erect filaments, elongated cylindrical and without paraphyses. Phylogenetic analyses based on COI-5P (545bp) reveal that P. subextensum are nested within Lithodermataceae and forms the same clade with P. roscoffense. The genetic divergences for COI-5P between them is 24.5%.

Laurencia is a red algal genus that was described by J.V. Lamouroux in 1813. The main characteristics of this genus have been known as the presence of four pericentral cells in an axial segment, secondary pit connections between adjacent epidermal cells, and the presence of corps en cerise in both epidermal and trichoblast cells. Additionally, the tetrasporangia are arranged in a parallel manner, and male branches feature terminal cup-shaped spermatangial pits. Currently, sixteen Korean Laurencia species have been reported based on their morphological characteristics. In this study, Laurencia decussata and L. pacifica have been added as new records to the Korean algal flora based on a combination of morphological observations and molecular analyses of rbcL sequences. Laurencia decussata has expanded from Australia and New Zealand to Korea, while the distribution of L. pacifica has expanded from USA and Mexico to Korea.

Neoporphyra kitoi Ma. Abe, N. Kikuchi, Tamaki, Tom. Sato, Murase, Fujiyoshi & Mas. Kobayashi has been known as an endemic species in Japan. Its high temperature tolerance suggests that it could be advantageous for cultivation. In this study, we collected it from the Ulleungdo island, Korea and transferred it into Pyropia for a new combination, identified as Pyropia kitoi (Ma. Abe, N. Kikuchi, Tamaki, Tom. Sato, Murase, Fujiyoshi & Mas. Kobayashi) D.J. Kim, T.O. Cho & B.Y. Won comb. nov. based on morphological and molecular analyses. Pyropia kitoi is also reported as a new record species in the list of Korean macroalgal flora. Although we didn’t observe the emergence of new blades from the rhizoidal cells, which is a key character for this species, our molecular analysis of rbcL revealed that our samples from Korea were congruent with “Neoporphyra kitoi” from Japan and were nested within the clade of Pyropia. The gene sequence divergence between the Korean and Japanese samples was 0-0.2%.

The genus Petroderma never been reported from the coast of Korea. In this study, our collection from Chaeseokang is matched with P. maculiforme morphologically. Petroderma maculiforme is characterized by having small irregular light to dark brown crusts, a basal layer of irregularly shaped cells giving rise to erect parallel filaments which easily separate with pressure, single chromatophore per cell, small spherical to cylindrical unilocular sporangia in a terminal position, and plurilocular sporangia narrower than erect filaments or wider and shorter than erect filaments in a terminal position. In addition, Hineksia sordida was also collected from Korea. It is mostly epiphytic and characterized by uniseriate filamentous thalli forming loose tangled masses, sparse and spiral branching, some long lateral branches, rhizoids occurring throughout the plant, plurilocular and unilocular sporangia scattered on separate plants. Our molecular analyses based on the rbcL gene reveal that our samples of P. maculiforme and H. sordida are nested within the clades of Petroderma and Hincksia, respectively. Therefore P. maculiforme and H. sordida are reported as new records from Korea based on morphological and molecular analyses.

Papenfussiella densa was described as Papenfussiella kuromo f. densa from Japan by Inagaki in 1958. P. densa has been recognized as an endemic and independent species based on the molecular analyses of type material without detailed morphological observations. In this study, Papenfussiella densa is reported as a new record from Dok-do, South Korea, based on morphological and molecular analyses. Papenfussiella densa is mainly characterized as having narrow, branched, slimy, and tomentose thalli with branchlets, partially hollow in the medulla of the middle part. The molecular analyses of the chloroplast rbc L-rbc S DNA sequence of the Papenfussiella densa sample from Korea revealed that it matched that of P. densa from Japan and was nested in the clade of Papenfussiella. There was only a 0.02% gene sequence divergence between the Korean and Japanese samples. We report P. densa as a new record from Korea and add this species to the list of Korean macroalgal flora.

Ralfsia longicellularis is known as an endemic species in Far East Asia. In this study, we report R. longicellularis as a new record from Korea based on morphological and molecular analyses. Molecular analyses based on plastid-encoded rbcL gene sequences and morpho-anatomical studies were undertaken on Ralfsia species, a poorly studied genus from Korea. Ralfsia longicellularis is mainly characterized by a dark brown thallus; 770-1200 μm thick, curved cells in the creeping and ascending parts of the filaments; basal layer and erect filament cells with a width-to-length ratio of 1 : 1.5 to 10; narrowshaped sporangia on-stalk cells at the base of the paraphyses; and mostly uniseriate plurilocular reproductive organs capped with 1-2 sterile cells. The R. longicellularis samples from Korea in this study were similar to ones collected from the type locality (Peter the Great Bay, Russia) in morphology. The rbcL analyses also revealed that our Korean R. longicellularis samples were placed in the same clade with Russian materials, within a Ralfsia clade but distinct from the congeners.

Acinetospora filamentosa and Microspongium stilophorae are reported as new records from South Korea based on morphological and molecular analyses. A. filamentosa is mainly characterized by having the sparsely branched erect filaments, the scattered meristematic zones, forming crampons, plurilocular sporangia on both prostrate filaments and lower part of erect filaments, and spherical to oval unilocular sporangia formed either sessile or with a pedicel. M. stilophorae is an epiphytic thalli mostly on Stilophora sp. It is characterized by prostrate filaments with irregular cells, short erect filaments with short ramuli, phaeophycean hairs, uniseriate plurilocular sporangia on the terminal part of erect filament. Our molecular analyses of rbcL and cox1 genes reveals that A. filamentosa and M. stilophorae are nested within the clades of Acinetospora and Microspongium, respectively.

Feldmannia chitonicola is reported as a new record from Korea based on morphological studies in laboratory-cultured materials and molecular analyses. F. chitonicola is mainly characterized by a small size (1-2 mm), erect filaments mostly unbranched, plurilocular sporangia produced on both prostrate and laterally on the basal part of erect filaments, and 2 types (lanceolate and ovate) of sporangia. In our cultures, sporangia production was slower at 10°C than in 16°C and 20°C. Our molecular analyses of rbcL and cox1 genes supported its independence from other congeners reported for Korea. This is the first report of F. chitonicola for western Pacific.

Acinetospora asiatica and Botrytella reinboldii are reported as two new records from S. Korea based on morphological studies and molecular analyses. A. asiatica is mainly characterized by the presence of sparsely branched uniseriate filaments with diffused meristematic zones, the formation of crampons at right angles, and the formation of plurilocular sporangia on both prostrate and erect filaments. B. reinboldii is characterized by the presence of irregularly alternating branched uniseriate filaments attached by rhizoids, and single or clustered plurilocular sporangia with a single opening. Molecular analyses of rbcL gene revealed that A. asiatica and B. reinboldii are placed within each clade of Acinetospora and Botrytella, respectively.

The morphology, anatomy and reproduction (tetra/bisporic and male) of Lithothamnion japonicum Foslie was studied, using holotype material and materials collected from Korea. Lithothamnion japonicum is characterized based on the presence of encrusting, warty to fruticose thallus, branched or unbranched short and cylindrical protuberances, conical shaped spermatangial conceptacles, branched (dendroid) spermatangial systems formed on floor, walls, and roof of conceptacle chamber, cylindrical shaped spermatangial conceptacle canal, 9-10 cell layered spermatangial conceptacle roof, raised tetra/bisporangial conceptacles without rims, flattened tetra/ bisporangial conceptacle pore plate, 16-50 pores on each pore plate, 6-8 rosette cells surrounded by each pore, pore canal lining filaments composed of tetra/bisporangial conceptacle roof, and buried senescent tetra/bisporangial conceptacles completely infilled with relatively large and irregularly arranged calcified sterile cells. In this study, we report a new record of Lithothamnion japonicum from Korean coasts.

Bryopsis africana and Pyropia kinositae are reported for the first time on the list of Korean marine algal flora based on integrated morphological-molecular study. Bryopsis africana from Korea is recognized with distinct main axes, robust thalli, pinnately and radially branched above, and basally denuded. Phylogenetic analyses revealed that B. africana was placed within a clade of Bryopsis. Bryopsis africana differs from B. corymbosa by 2.7% gene sequence divergence. Pyropia kinositae is characterized by oblong to lanceolate thalli, entire margin, purplish red in color, twice as long as broad cells in transversal section view. Phylogenetic analyses revealed that P. kinositae was placed within a clade of Pyropia. Pyropia kinositae differs from P. tenera by 1.5-1.8%, P. ishigecola by 1.2-1.3%, and P. yezoensis by 1.5-1.8% gene sequence divergence respectively.

Detailed morphological studies and molecular analyses based on plastid-encoded rbcL gene sequences were undertaken on Peyssonnelia species, a poorly known genus from Korea. We report new records for the Korean coast, Peyssonnelia harveyana and P. rumoiana. Peyssonnelia harveyana is chiefly characterized by P. rubra-type anatomy, closely packed perithallial filaments in firm matrix, hypothallial filaments arranged in parallel rows, thalli with appressed margins, hypobasal calcification, and unicellular rhizoids. Peyssonnelia rumoiana is principally characterized by two vegetative features, hypothallial filaments arranged in a polyflabellate layer, and perithallial filaments arising from the whole upper surface of each hypothallial cell (Peyssonnelia rubra-type anatomy). Our rbcL analyses revealed that P. harveynana and P. rumoiana were placed within a clade of Peyssonnelia. We also propose the new combination, Sonderophycus cauliferus comb. nov., for previous Peyssonnelia caulifera. Phylogenetic analyses revealed that our S. cauliferus was placed within a clade of Sonderophycus.