Molecular phylogeny of foliose Halymenia and Austroepiphloea (Halymeniaceae, Rhodophyta) from the Indo-Pacific, with the description of Halymenia taiwanensis sp. nov.

Many species of Halymenia from the Indo-Pacific have been described in the past decade, but their phylogenetic relationships are not well discussed. In this study, we inferred these relationships for the available species of Halymenia with an emphasis on the foliose species from the western Pacific Ocean and Western Australia based on rbcL and nuclear-encoded LSU rDNA sequence analyses. Our analyses show that most foliose Halymenia from the Indo-Pacific are clustered in a natural assemblage that also includes a new species (Halymenia taiwanensis sp. nov.) found in northern Taiwan, as well as the monospecific genus Austroepiphloea (single species A. bullosa) from Western Australia. The architecture of carpogonial branch (composed of a two-celled carpogonial branch and two orders of ampullar filaments, and a basal, nutritive cellular cluster) and auxiliary cell ampullae in Halymenia taiwanensis is similar to that found in the generitype H. floresii. We therefore propose the new combination Halymenia bullosa comb. nov. (basionym Schizymenia. bullosa), a species closely related to H. taiwanensis both genetically and morphologically. However, H. taiwanensis can be separated from H. bullosa by its thinner blades and surface bladelets, and by lacking a long cartilaginous stipe. Based on the rbcL phylogeny, most foliose Halymenia are seemingly more range-restricted than previously thought, except for a few species that are shown to have a wide distribution in the Western Pacific and Indian Oceans. In addition, H. dilatata, a species widely recorded in the Western Pacific Ocean, may include cryptic species and requires further investigation.

Automated summary

This study analyzed the phylogenetic relationships of Halymenia species from the Indo-Pacific region, and found that most foliose Halymenia species are clustered in a natural assemblage. The study also discovered a new species and revealed that some species have a more restricted distribution than previously thought. Additionally, the widely distributed Halymenia dilatata may include cryptic species that require further investigation.