Morpho-anatomical study of Sargassum (Fucales, Phaeophyceae) diversity reveals noteworthy collections and range extensions from southwestern Vietnam

Sargassum is widely distributed marine brown seaweed taxon with high diversity and taxonomic debates. To improve our understading of the Sargassum flora of southwestern Vietnam, more than 108 specimens of Sargassum were collected in the Phu Quoc Island and nearby localities. Five species were newly recorded in southwestern Vietnam based on morphoanatomical evidence; S. cinereum, S. confusum and S. siliquosum were limited to southwestern Vietnam, and ranges of S. feldmannii and S. microcystum were extended to the Phu Quoc Island. Their descriptions, illustrations, and voucher specimens are provided in the present study. The findings are useful for future monitoring surveys and have conservation and ecosystem applications.