Abstract Lithophyllum is a highly diverse and widely distributed genus of non-geniculate coralline algae. Despite its ecological importance, a comprehensive taxonomic treatment of Lithophyllum species in Korea remains lacking, primarily due to substantial unresolved cryptic diversity within the genus. In this study, we describe Lithophyllum jejuensis based on an integrated taxonomic approach combining molecular phylogenetic analyses with detailed morpho-anatomical observations of specimens from Korea. Phylogenetic analyses of plastid markers ( psb A and rbc L) resolved L. jejuensis as a distinct lineage. Morpho-anatomically, the species exhibits a multilayered, encrusting growth form with successive applanate branches, bistratose margins, and predominantly palisade basal (hypothallial) cells. Lithophyllum jejuensis resembles L. prototypum (originally described from the U.S. Virgin Islands), but differs from the holotype in having widely triangular tetrasporangial conceptacle pore canals that taper toward the thallus surface. Additionally, L . jejuensis can be distinguished from Korean L. neo-okamurae and L. okamurae by an exclusively adherent, encrusting growth form with applanate branches, bistratose margins composed of palisade cells, and larger tetrasporangial conceptacle chamber dimensions. These results reaffirm the importance of integrative taxonomy in elucidating the cryptic diversity of Korean Lithophyllum .
Lee et al. (2026) studied this question.