Polysiphonia hainanensis was previously described from Hainan, China, but DNA sequence had never been provided and its phylogenetic position in Polysiphonieae has not been clear so far. The classification of Polysiphonieae has changed recently based on the molecular analyses and detail morphological anatomy, consequently, the generic assignment of some species must be reassessed. In this study, we analyzed phylogenetic relationships of P . hainanensis and the related taxa in Polysiphonieae and Streblocladieae based on rbc L sequences, with specimens collected from the type locality and the area around. Two genetic types were detected, and formed a clade with Bryocladia thyrsigera with strong bootstrap support, in which the divergence was less than 0.81％. Furthermore, based on morphological analyses, we found characteristics of Chinese specimens, number of pericentral cells, percurrent axis, determinate branchlets, branching pattern, spermatangial axes development, and arrangement of tetrasporangia, etc., were consistent with those of Bryocladia . Combined with morphological and molecular analyses, P . hainanensis was taken a synonymous of B . thyrsigera , and gametophytes of this species were found from China for the first time.