Carpopeltis maillardii has been regarded as a widely distributed species in the Indo-Pacific region. In this study, we analyzed the genetic diversity of C. maillardii and related species collected from Taiwan and the Indian Ocean based on rbcL sequences, in order to elucidate species boundaries, diversity, and biogeographic patterns. Our analyses show that C. maillardii specimens are only distantly related to the genus Carpopeltis (type: C. phyllophora) but instead form a clade together with species of Yonagunia. We therefore propose the new combination Yonagunia maillardii comb. nov. In addition, two new species (Yonagunia palmata sp. nov. and Yonagunia taiwani-borealis sp. nov.) are described from Taiwan. The close relationship of Yonagunia to Grateloupia is corroborated by detailed observations of the female reproductive structures, which demonstrate that the development of auxiliary cell ampullae before and after diploidization is similar to that of Grateloupia sensu stricto. Namely, the ampullae are composed of only two orders of unbranched filaments in which only a few ampullar cells are incorporated into a basal fusion cell after diploidization of the auxiliary cell and the pericarp consists almost entirely of secondary medullary filaments. Of all Yonagunia species, Y. maillardii has the widest distribution in the Indo-Pacific, and can be identified in the field by its relatively thin, feathery, and highly branched morphology. Most other species, including those that occur in Taiwan, are seemingly more range-restricted. Our phylogenetic analyses resulted in a well-resolved phylogeny of Yonagunia, with an origin estimated in the Eocene–Oligocene, and diversification of species mainly in the Miocene. |
