Accurately identifying species is the basis of all biological studies. There has been much confusion in the identification of Grateloupiacean species, which have finely pinnate gross morphology similar to Grateloupia filicina (the type species of the family). The objective of this study was to comprehensively investigate species identification and distribution of G. filicina-like species in the Northwest Pacific, based on the rbcL sequences. A total of 118 specimens from 78 sites in Korea and Japan were collected from 2001 to 2021 and analyzed for their rbcL sequences. Additional 341 sequences downloaded from the GenBank were included in our comprehensive dataset. Based on these sequences, we documented the nomenclatural history and geographical distribution of the species, and commented on the application of species name. G. asiatica was the most abundant G. filicina-like species in the Northwest Pacific, and its high degree of morphological variation caused many misidentifications. In particular, G. dalianensis, G. serra and G. variata require reconsideration of their conspecificity with G. asiatica using more specimens from China. By contrast, G. oligoclora was presumed to be a heterotypic synonym of G. subpectinata. The occurrence of G. acuminata, G. ramosissima, and G. livida in Korea resulted from misidentifications with other species.

Accurately identifying species is the basis of all biological studies. There has been much confusion in the identification of Grateloupiacean species, which have finely pinnate gross morphology similar to Grateloupia filicina (the type species of the family). The objective of this study was to comprehensively investigate species identification and distribution of G. filicina-like species in the Northwest Pacific, based on the rbcL sequences. A total of 118 specimens from 78 sites in Korea and Japan were collected from 2001 to 2021 and analyzed for their rbcL sequences. Additional 341 sequences downloaded from the GenBank were included in our comprehensive dataset. Based on these sequences, we documented the nomenclatural history and geographical distribution of the species, and commented on the application of species name. G. asiatica was the most abundant G. filicina-like species in the Northwest Pacific, and its high degree of morphological variation caused many misidentifications. In particular, G. dalianensis, G. serra and G. variata require reconsideration of their conspecificity with G. asiatica using more specimens from China. By contrast, G. oligoclora was presumed to be a heterotypic synonym of G. subpectinata. The occurrence of G. acuminata, G. ramosissima, and G. livida in Korea resulted from misidentifications with other species.