Morphological and molecular characteristics of Homoeostrichus formosana sp. nov. (Dictyotaceae, Phaeophyceae) from Taiwan

Background: In the marine brown macroalgae, the morphological characters are highly similar between two widely distributed genera, Homoeostrichus and Zonaria (Dictyotaceae), thereby resulting in the difficulty of exploring their hidden biodiversity. Owing to the help of the molecular tools, it is now easy for scientists to objectively describe a new species in nature. In this study, we make a description on the Homoeostrichus formosana sp. nov. from Taiwan, Indo-Pacific Ocean based on the morphological evidence and molecular data. Results: Our morphological observations revealed that this species has marginal row of apical cells responsible for thallus growth and the thallus with four layers of cells except the marginal regions. The cortical cell lies upon each medullary cell in transverse section, and two cortical cells upon each medullary cell in longitudinal section. Tetrasporangium is developed from cortical cell with stalk cell and singly scattered over the thallus surface, and has no indusia and paraphyses. Molecularly, the phylogenetic trees based on SSU, psaA, psbA, and rbcL gene sequences supported that Homoeostrichus species are closely related to Exallosorus species and clearly separated from each others in addition to Zonaria species. Conclusions: Homoeostrichus formosana sp. nov. can now be clearly distinguished from E. harveyanus and Japanese H. flabellatus.