Occurrence of the calcifying brown alga <i>Newhousia</i> (Dictyotales, Phaeophyceae) in Southeast Asia

The calcifying brown algal genus Newhousia (Dictyotales, Phaeophyceae) was previously reported from scattered Pacific localities, including Hawaii and Guam (Northern Hemisphere), French Polynesia, Papua New Guinea, and Vanuatu (Southern Hemisphere). We report here the occurrence of Newhousia from Southeast Asia, based on collections from Nha Trang Bay, Vietnam, representing a record from continental Asia and the westernmost occurrence of the genus. Multigene molecular analyses (psbA, rbcL, cox1, and cox3) identified the Vietnamese specimens as Newhousia imbricata. Morphological observations corroborated its diagnostic vegetative proliferation by eruption of new blade primordia. These findings extend the known distribution of Newhousia to Southeast Asia and highlight the ecological breadth of N. imbricata. They also emphasize the urgent need for expanded surveys across the Indo-Pacific to better resolve the genus's biogeography and diversity, which in turn will provide the foundation for deeper investigations into its dispersal mechanisms, evolutionary history, and reproductive biology.