Evolutionary history of Afro-Madagascan Ixora

Ixora regalis
Ixora regalis

The pantropical genus Ixora is one of the largest genera in Rubiaceae, with approximately 530 species. Tosh et al. conduct phylogenetic analyses based on four plastid and two nuclear ribosomal markers to infer the historical biogeography of Afro-Madagascan Ixora species. They find that Madagascan Ixora do not form a monophyletic group, but are represented by two separate lineages of different ages, with at least one dispersal event occurring from East Africa into Madagascar in the late Pliocene. Both lineages of Madagascan Ixora exhibit morphological characters that are rare throughout the rest of the genus, including pauciflorous inflorescences and extreme corolla tube length.