PHYLOGENY AND CLASSIFICATION OF THE SPECIES-RICH PANTROPICAL SHOWY GENUS IXORA (RUBIACEAE-IXOREAE) WITH INDICATIONS OF GEOGRAPHICAL MONOPHYLETIC UNITS AND HYBRIDS
Résumé
Species-rich genera often have various confl icting circumscriptions from independent regional fl ora treatments. Testing the monophyly of these groups of plants is an important step toward the establishment of a phylogenetic classifi cation. The genus Ixora of the tribe Ixoreae in the subfamily Ixoroideae (coffee family or Rubiaceae) is a species-rich pantropical genus of ca. 500 species. Phylogenetic analyses of Ixoreae based on combined sequence data from one nuclear (nrETS) and two chloroplast ( rps16 and trnT-F ) markers reveal the paraphyly of Ixora as presently delimited and also show that the tribe can be subdivided into three major clades: the Mascarene/neotropical/Malagasy/African clade, the Pacifi c clade, and the Asian clade. Given the lack of morphological synapomorphies supporting the different Ixora clades and the morphological consistency of the ingroup taxa, we propose a broad circumscription of Ixora including all its satellite genera: Captaincookia , Doricera , Hitoa , Myonima , Sideroxyloides , Thouarsiora, and Versteegia . The current infrageneric classifi cation of Ixora is not supported. The different Ixora subclades represent geographical units. Nuclear and chloroplast tree topologies were partially incongruent, indicating at least four potential natural hybridization events. Other confl icting positions for the cultivated species are most likely due to anthropogenic hybridization.