Subtribe Oncospermatinae (Arecaceae: Arecoideae: Areceae) is a diverse group of spiny Old World palms. The subtribe includes Oncosperma, a widespread Asian genus of five species, along with seven monotypic genera, all endemic to the Seychelles and Mascarene Islands of the western Indian Ocean. A phylogenetic analysis was conducted in order to test the monophyly of subtribe Oncospermatinae with respect to other Old World genera of tribe Areceae. A matrix of 38 morphological characters was scored for 29 taxa, including 11 species of the Oncospermatinae. A single most parsimonious tree was found, resolving the subtribe as a polyphyletic group of two distinct clades. One clade containing Acanthophoenix, Deckenia, Oncosperma, and Tectiphiala was placed as sister to a large group that includes members of subtribes Archontophoenicinae, Arecinae, Iguanurinae, and Ptychospermatinae. The other clade of Oncospermatinae, including the Seychelles endemic genera Nephrosperma, Phoenicophorium, Roscheria, and Verschaffeltia, was resolved as sister to the Madagascar endemic subtribe Masoalinae, and may have arisen in the western Indian Ocean region.