Morpho‐anatomical and genetic variation of <i>Lithophyllum neo‐okamurae</i> and <i>L. okamurae</i> (Corallinales, Corallinophycidae, Rhodophyta) from Jeju Island, Korea

SUMMARY Lithophyllum Philippi (Corallinales, Corallinophycidae, Rhodophyta) is a diverse genus of non‐geniculate coralline algae. Lithophyllum neo‐okamurae and L. okamurae are commonly found in the intertidal and subtidal zones of Jeju Island, Korea, where they contribute to local benthic communities. Despite their ecological importance, their morpho‐anatomical and genetic variation remain poorly understood in this region. We investigated these two species through morpho‐anatomical and molecular analyses ( psb A and rbc L) based on specimens collected from 13 sites around Jeju, Korea. Lithophyllum neo‐okamurae exhibited both unattached, free‐living (rhodolith) and attached forms, each showing distinct distributions associated with local hydrodynamic and substrate conditions. Molecular analyses revealed distinct haplotypes corresponding to the two forms, and morpho‐anatomical analyses detected statistically significant differences in tetrasporangial conceptacle chamber dimensions (diameter and height) between them. In contrast, L. okamurae occurred exclusively as unattached rhodoliths and was mainly distributed in deeper subtidal rhodolith beds compared with L. neo‐okamurae . Our findings demonstrate form‐related morpho‐anatomical and genetic differentiation in L. neo‐okamurae and underscore the ecological role of L. neo‐okamurae and L. okamurae as major rhodolith‐forming species in Jeju, Korea.