Ruppiamaritima (widgeon grass) has been identified phylogenetically for the first time from West Africa (Santiago Island, Cape Verde). Genetic markers distinguished this species from the tetraploid Ruppia cf. maritima previously known from West Africa. Taxonomic description, photographs and molecular phylogenetic classification are provided here. The results show that, in Cape Verde, the species is phylogenetically closer to European and northeast American than to Indo-Pacific populations. This study extends the known distribution of R. maritima, an ecosystem structuring species that provides essential habitat for threatened animals.