A molecular phylogeny of Acronychia, Euodia, Melicope and relatives (Rutaceae) reveals polyphyletic genera and key innovations for species richness.

We present the first detailed phylogenetic study of the genus Melicope, the largest genus of the Citrus family (Rutaceae). The phylogenetic analysis sampled about 50% of the 235 accepted species of Melicope as well as representatives of 26 related genera, most notably Acronychia and Euodia. The results based on five plastid and nuclear markers have revealed that Acronychia, Euodia and Melicope are each not monophyletic in their current circumscriptions and that several small genera mainly from Australia and New Caledonia need to be merged with one of the three genera to ensure monophyly at the generic level. The phylogenetic position of the drupaceous Acronychia in relation to Melicope, which has capsular or follicular fruits, remains unclear and Acronychia might be a separate genus or a part of Melicope. The seed coats of Melicope, Acronychia and related genera show adaptations to bird-dispersal, which might be regarded as key innovations for species radiations. Euodia and its relatives, which lack these adaptations, include only about 20 species while the Melicope-Acronychia group consists of about 340 species. The drupaceous genera Comptonella, Dutaillyea, Picrella and Sarcomelicope are nested within Melicope and need to be merged with Melicope. The expanded genus is a prime example of the artificial classification system of Engler, who defined Rutaceous subfamilies mainly based on gynoecial and fruit characters.