Integrative Taxonomy of Harveylithon (corallinales, Rhodophyta) Reveals Three New Species from Korea and Expanded Diversity in the Northwestern Pacific

Non-geniculate coralline genus Harveylithon includes 12 species worldwide. In this study, we propose three new species, Ha. koreanum sp. nov., Ha. longiforme sp. nov., and Ha. planiforme sp. nov., based on integrative molecular and morphological analyses. These three new species share the diagnostic morphological characters of Harveylithon, including a monomerous, non-coaxial thallus construction with perithallial cells oriented perpendicularly to the surface; a hypothallial layer composed of rectangular cells aligned parallel to the substratum; and the presence of trichocytes occurring singly, in pairs, or in clusters. Our phylogenetic analyses of a concatenated four-gene data set (COI + rbcL + psbA + SSU rRNA) clearly resolved the three new species within Harveylithon, each forming a well-supported and distinct lineage. The topologies of the individual-gene phylogenies based on the psbA and the SSU rRNA genes were largely congruent and supported these relationships, whereas phylogenetic trees based on the rbcL and COI genes did not recover Harveylithon as monophyletic, with Dawsoniolithon species nested within the Harveylithon clade. Interspecific sequence divergences between new species and their congeners were 6.3%-13.7% for the COI gene, 0.8%-9.8% for the psbA gene, and 1.8%-14.6% for the rbcL gene. Harveylithon koreanum sp. nov. and Ha. planiforme sp. nov. are currently known from only Jeju Island in Korea, whereas Ha. longiforme sp. nov. was identified from both Jeju Island, Korea, and India, indicating that it may have a broad Indo-Pacific distribution. In addition, we newly generated the psbA gene sequence from the generitype, Ha. rupestre (TRH A3-149) and incorporated it into our molecular data set to stabilize the phylogenetic circumscription of the genus.