The vegetative and reproductive morphology of some parasitic Janczewskia Solms-Laubach species including the type species was examined based on specimens collected from various localities around the world. In J. gardneri Setchell et Guernsey on Osmundea spectabilis (Postels et Ruprecht) Nam from California, secondary pit connections are not found between epidermal cells and vegetative axial cells have two pericentral cells. As its host, J. gardneri also has a typical filament type male structure in an apical urn-shaped pit of branches rather than the trichoblast type in other species including the type J. verruciformis Solms-Laubach and tetrasporangial origin of epidermal cells rather than pericentral cells. These significant differences between the species suggest that J. gardneri should be separated from the genus Janczewskia. Based on this morphological data, the section Heterojanczewskia Setchell including J. gardneri, together with an emendation of the generic delineation of Janczewskia, is elevated to the genus level. Relevant nomenclatural changes for some Janczewskia species are also included here.

A marine red algal species was collected from Pyengdae-ri, Gujwa in Jeju, Korea during a survey of marine algal flora. This alga shares the generic features of Callophyllis (Gigartinales, Kallymeniaceae), and is characterized by erect and membranous thalli, branches dichotomously or trichotomoulsy divided, margin somewhat undulate or entire and tetrasporangia scattered irregularly in the cortex. In a phylogenetic tree based on rbc L sequences, the Korean alga nests in the same clade as C. mageshimensis originally described from Japan. The genetic distance between both sequences within the clade was 0.0-0.1%. Based on the morphological and molecular data, the alga was identified as Callophyllis mageshimensis. This is the first record of C. mageshimensis in Korean marine algal flora.

A marine red algal species was collected from Honghyeon-ri, Namhae located on the southern coast of Korea during a survey of marine algal flora. This alga shares the generic features of Chondrus, and is characterized by short and thin, canaliculated and crisped fronds as C. retortus. Tetrasporangia are developed from shallow medullary cells on both sides of branches. In a phylogenetic tree based on rbcL sequences, the Korean alga nests in the same clade as C. retortus originally described from Japan. The genetic distance between both sequences within the clade was calculated as 0.0-0.1%. Based on the morphological and molecular data, the alga is identified as Chondrus retortus. This is the first record of C. retortus in Korean marine algal flora.

A marine red algal species was collected from Uljin, located on the eastern coast of Korea, during a survey of marine algal flora. This alga shares the generic features of Plocamium, and is characterized by linear, flat and thin thalli with narrow axes, branches developing in alternating pairs from margins of the axes, two to four times alternately pinnately branching, linear or occasionally adaxially curved lowermost branchlets and distinctly and compactly clustered stichidia. In a phylogenetic tree based on rbcL sequences, the Korean alga nests in the same clade as P. serrulatum. The genetic distance between both sequences within the clade was calculated as 0.0-0.2%. Based on the morphological and molecular data, this Korean species is identified as P. serrulatum described originally from Taiwan. This is the first record of P. serrulatum in Korean marine algal flora.

A marine green algal species (Chlorophyta) was collected from the eastern coast of Korea. It is morphologically characterized by monostromatic thallus, usually undulate and entire margins, cap-like chloroplast and several pyrenoids per cell. In a phylogenetic tree based on molecular data, the Korean alga nests in the same clade as Monostroma alittorale originally described from Japan, as a sister clade of M. grevillei from France. The genetic distance for ITS (Internal Transcribed Spacer) sequences among Monostroma species ranges from 2.3% to 38.2%. The value between the Korean entity and M. alittorale was calculated as 0.01%, considered to be intraspecific divergence. This Korean entity is identified as Monostroma alittorale based on morphological and molecular analyses. This is the first record of M. alittorale in Korea.

A marine ulvalean species (Chlorophyta) was collected from the eastern coast of Korea. This species is morphologically characterized by a distromatic, dark to medium green and mostly irregularly orbicular or irregularly expanded thallus with entire or undulate margin without serrations. Vegetative cells are irregularly polygonal with distinctly rounded corners in shape, and have chloroplast completely covering the outer cell wall and one to two pyrenoids per cell. In a phylogenetic tree based on ITS (Internal Transcribed Spacer) sequences, this Korean alga nests in the same clade with Ulva sublittoralis, as a sister clade of U. californica, U. flexuosa and U. tanneri, which share the irregularly orbicular or expanded thallus normally without teeth cells. The genetic divergence between them is intraspecific within Ulva. Accordingly, it is identified as U. sublittoralis based on the morphological and molecular data. This is the first record of Ulva sublittoralis in the Korean marine algal flora.

A marine algal species was collected from Sacheonjin, Gangneung located on the eastern coast of Korea during a survey of marine algal flora. This alga shares the generic features of Membranoptera belonging to the subfamily Delesserioideae and is characterized by the presence of combined features of membranous, monostromatic thalli attached by a solid discoid holdfast, blades with a conspicuous terete stipe-like midrib and microscopic lateral veins, entire margins, irregularly alternate to dichotomous branching, and obtuse apices growing apically. In a phylogenetic tree based on rbcL sequences, the Korean alga nests in the same clade with M. alata from the eastern North Atlantic. The genetic distance between both the sequences within the clade was calculated as 0.0%. Based on the morphological and molecular analyses, this Korean species is identified as the generic type, M. alata. This is the first record in the list of Korean marine algal flora.

During a survey of marine algal flora, a red algal species was collected from Giseong, Uljin located on the eastern coast of Korea. This species has the generic features of Cryptonemia belonging to Halymeniaceae, and is characterized by the presence of erect foliose thalli arising from a discoid holdfast, somewhat fan-shaped blade with an evanescent midrib at the base, narrow main axes with blade-like wings of slightly undulate margin, a perennial stalk, and entwined filamentous medulla with refractive stellate cells. In a phylogenetic tree based on rbcL sequence, the Korean alga nests in the same clade with C. lomation from France and C. seminervis from Spain. Genetic divergence among the sequences within the clade was not recognized thus suggesting that both the species are conspecific. The name C. lomation considered to be valid nomenclaturally is accepted for the entity. Based on the morphological and molecular analyses, the Korean alga is identified as C. lomation, originally described from Italy. This confirms the occurrence of C. lomation in Korea. The species appears to be distributed in the temperate region influenced more or less by the North Korea Cold Current.

Two siphonous green algae were collected from the eastern coast of Korea. These species share the typical features of Derbesia sporophytes, such as erect and prostrate siphonous filaments and the presence of basal septum in lateral branches. One is characterized by the combined features of a relatively small tufted sporophytic thalli arising from a rhizoidal base, subdichotomously branched filaments with a basal septum and one pyrenoid per subspherical to lenticular chloroplast. The other shows a larger sporophytic thallus, sparsely subdichotomously branched filaments with a basal septum and one pyrenoid per spherical chloroplast. In a phylogenetic tree based on rbcL sequence, the two above-mentioned Korean algae nest in the same clades as Derbesia minima and D. indica, respectively. The genetic distance between the sequences within the clades was 0.5- 0.8%, which is considered to be included in the intra-specific range for the genus. These two siphonous Korean algae are identified as D. minima and D. indica, respectively, based on the morphological and molecular analyses. These species are newly recorded in the Korean marine algal flora herein.

A marine algal species belonging to Gigartinales was collected from Geoje, Korea. This shares the generic features of Ahnfeltiopsis, such as multiaxial thalli with a compact and pseudoparenchymatous medulla, densely cytoplasmic secondary medullary cells around immersed cystocarps with a carpostome, and is distinct from similar species within the genus by a combined feature of small (up to 4 cm tall) and tuft thalli, compressed to subcompressed branches except for ultimate branchlets and base of main axes, cartilaginous in texture, dichotomous branches, rarely produced proliferations, absence of hypha-like filament in the medulla and internal cystocarps with a carpostome. In phylogenetic tree based on rbcL sequence, the Korean species nests in the same clade with Ahnfeltiopsis linearis. The genetic distance between both sequences within the clade was 1.5%, considered to be within the intra-species range for the genus. This morphological and molecular evidence confirms the Korean alga to be identified as A. linearis originally described from California. This is the first record of A. linearis in Korea.

The delesseriacean parasitic red algal Asterocolax species was collected from Jindo in the southern coast of Korea. This parasitic species found on Pseudopolyneura japonica. And it is distinct from other species of Asterocolax with more or less denticulate branches when matured. This Korean entity is identified as Asterocolax denticulatus (Tokida) Feldmann & Feldmann (Delesseriaceae, Rhodophyta) based on these features. This is the first record of A. denticulatus in Korea.

A marine brown alga was collected from Geoje, located on the southern coast of Korea. This species shares the generic features of Dictyota and is morphologically characterized by the combined features of erect or prostrate thallus with smooth margin, dichotomous to subdichotomous branches not twisted at the terminal part, absence of surface proliferations, 1-3 cell layered cortex and unilayered medulla, and lack of involucrum in sporangia subtended by a single stalk cell. In a phylogenetic tree based on rbcL sequences, this species nests in the same clade with Dictyota bartayresiana. The genetic distance between both sequences within the clade was calculated as 1.2%, considered to be within the intra-species range for the genus. Based on these morphological and molecular analyses, this Korean alga is identified as D. bartayresiana described originally from the West Indies. This is the first record of D. bartayresiana in Korea.

A marine ulvalean species (Chlorophyta) was collected from Imgok, which is located on the eastern coast of Korea. This species is morphologically characterized by distromatic, filiform to strap compressed or tubular thallus. Many branches were found near the base, but lacked proliferations. Cells were longitudinally aligned in the younger part of the branch and were disordered in the older part of the branch. A cap-like parietal chloroplast with one or two pyrenoids was contained in each cell. In a phylogenetic tree based on ITS and rbcL sequences, this species was nested in the same clade as Ulva torta and U. clathratioides from Australia, but formed a sister clade to U. torta from Japan. However, the genetic divergence between them was included in an intraspecific variation range within Ulva. This finding suggests that U. clathratioides should be reduced to a synonym of U. torta. Accordingly, the Korean alga was identified as U. torta based on the morphological and molecular data. This investigation is the first record of U. torta in the Korean marine algal flora.