Revision of Chondrophycus in Korea with description of Chondrophycus coreanus sp. nov. (Ceramiales, Rhodophyta)

Three Chondrophycus species have been recorded primarily based on morphology from Korea: Chondrophycus cartilagineus , C. kangjaewonii, and C. undulatus. In this study, we collected 25 Chondrophycus samples from Korea and Japan, and confirmed the presence of Chondrophycus cartilagineus, C. kangjaewonii, and C. undulatus among them. We here propose a new species, Chondrophycus coreanus sp. nov., to the Korean floral list. Chondrophycus coreanus sp. nov. is characterized by terete to partially compressed thalli, cortical cells projecting near the branchlet apex, absence of secondary pit connections between cortical cells, thickened medullary cell walls without lenticular thickenings, and a cystocarp with a protuberant ostiole. Our phylogenetic analyses, based on the sequences of the rbcL and 5' region of cytochrome c oxidase subunit I (COI-5P) genes, showed that C. coreanus is nested within the Chondrophycus genus with full support, forming a distinct clade. Chondrophycus coreanus sp. nov. exhibits significant genetic divergences from other Chondrophycus species, ranging from 4.2–9.5% for rbcL and 5.5–11.6% for COI-5P. The genetic differences were 5.3–7.4% for rbcL and 6.1–10.4% for COI-5P between C. coreanus sp. nov. and other Korean Chondrophycus species. Chondrophycus coreanus sp. nov. is distributed in Korea, Japan, and Hawaii, USA.