Abstract: Grateloupia huangiae S.-M. Lin & H.-Y. Liang sp. nov. was previously recorded as G. okamurae Yamada [currently recognized as Polyopes lancifolius (Harvey) Kawaguchi & H.W. Wang] in Taiwan. Molecular phylogenetic analysis shows that G. huangiae is unrelated to P. lancifolius but is closely related to Grateloupia taiwanensis S.-M. Lin & H.-Y. Liang. Although G. huangiae superficially resembles P. lancifolius in having a leafy thallus and short proliferations borne on the thallus surface, the structure of the auxiliary-cell ampulla is very different. The auxiliary-cell ampulla of G. huangiae is composed of three orders of unbranched filaments before diploidization, each of which is 11–13 cells long. The auxiliary cell is the first cell of the third-order ampullar filament, which is cut off from the first cell of the second-order ampullar filament. This type of auxiliary-cell ampulla is the same as that found in G. taiwanensis. On the other hand, P. lancifolius has a more complex auxiliary-cell ampulla in which the ampullar filaments may bear up to five to six orders of branches before diploidization. A detailed study of the development of auxiliary-cell ampullae before and after diploidization is needed in other species and genera within the Halymeniaceae to better delineate generic concepts in the family.