Background and aims The tribe Danaideae (Rubiaceae) is almost

exclusively endemic to the Western Indian Ocean Region (WIOR), encompassing the

genera Danais, Payera and Schismatoclada that occur in humid and sub-humid

climates. Much of the species diversity is endemic to restricted, remote and/or

mountainous areas of the WIOR, and recent field work on Madagascar indicates

substantial unknown diversity of the Danaideae. Further, the monophyly of the

Malagasy genera Payera and Schismatoclada has been questioned in previous work,

species delimitations and phylogenetic relationships within the genera are poorly

understood, and distribution and evolution of gross morphological features have not

been assessed.

 Methods We conducted morphological investigations, and produced robust

phylogenies of Danaideae based on nuclear and plastid sequence data from 193

terminals. Ample plant material has been newly collected in the WIOR for the

purpose of the present study, including potentially new species unknown to science.

We performed Bayesian non-clock and relaxed-clock analyses employing three

alternative clock models of a dataset with a dense sample of taxa from the entire

geographic ranges of Danaideae. Based on the results, we discuss species diversity

and distribution, relationships, and morphology in Danaideae.

 Key results Our results demonstrate the monophyly of Danaideae, its three

genera, and 43 species. Nine species are resolved as non-monophyletic. Many

geographically distinct but morphologically heterogeneous lineages were identified,

and morphological features traditionally considered diagnostic of subgroups of the

genera, used e.g. in species identification keys, are not clade-specific.

 Conclusions Our results demonstrate that Madagascar contains ample hereto

undocumented morphological and species diversity of Danaideae. Our novel approach

to perform molecular phylogenetic analyses as a precursor to taxonomic revisions

provides numerous benefits for the latter. There are tentative indications of parallel

northward diversification in Payera and Schismatoclada on Madagascar, and of

geographic phylogenetic clustering despite the anemochorous condition of Danaideae