Phylogeny, species diversity and biogeographic patterns of the genus Tricleocarpa (Galaxauraceae, Rhodophyta) from the Indo-Pacific region, including T. confertus sp. nov. from Taiwan

Among four different genera in Galaxauraceae, species diversity of the genus Tricleocarpa Huisman & Borowitzka is underestimated and requires further examination. In this study, we explored a molecular phylogeny of Tricleocarpa with an emphasis on Taiwan species and reassessed species diversity of the genus from the Indo-Pacific region based on analyses of rbcL and COI-5P sequences and morphological observations. The molecular analyses showed that species of Tricleocarpa examined are grouped into seven clades: six clades in the T. cylindrica group (the T. cylindrica complex, T. confertus, T. jejuensis, T. natalensis and two uncharacterized T. ‘cylindrica’ clades) and one clade as the T. fragilis group. Overall, at least 12 species in Tricleocarpa were detected from the Indo-Pacific region, including a new species, T. confertus S.-L. Liu & S.-M. Lin, from Taiwan. Among them, T. confertus can be separated from other species of Tricleocarpa by a thallus consisting of dichotomous or trichotomous, articulated and moniliform branches with smooth surfaces, constrictions at nodes and slightly anti-triangular in shape. The cystocarp morphology of T. confertus is similar to the T. cylindrica group by having paraphyses intermixing with gonimoblast filaments. Recognition of this new species from other species is also supported by the DNA-based, algorithmic species delimitation approaches. With the combination of molecular phylogeny and species diversity reassessment, our phylogeographic analysis supported a trend that species in the T. fragilis group are restricted in their distribution to subtropical and tropical areas whereas species in the T. cylindrica group have a wide distribution, ranging from temperate through to tropical areas.