Rinorea Aublet is a pantropical genus of shrubs and small trees and is the second most species-rich genus in the Violaceae with an estimated 225—275 species. The species in Madagascar and the Comoro Islands have not been revised since 1949, nor has there been an adequate understanding of infrageneric groupings, phylogeny, and biogeography for the entire genus. The goals of this study were: 1) taxonomic revisions of two species-rich infrageneric groups of Malagasy and Comorian Rinorea (R. subsect. Verticillatae and the R. arborea species group), 2) a revised infrageneric classification of the African and Malagasy species, 3) phylogenetic reconstruction inferred from chloroplast DNA sequences with genus-wide taxon sampling, and 4) biogeographic inferences of the Malagasy species.
The revision of the genus Rinorea arborea group and R. subsect. Verticillatae, resulted in nine and three new species, respectively. Forty-one species of Rinorea are here recognized for Madagascar and the Comoro Islands. A newly proposed infrageneric classification of African and Malagasy Rinorea—based on morphometric and molecular phylogenetic evidence—recognizes 11 taxonomic sections, including four new sections: Arboreae, Squamosae, Angustifoliae, and Ellipticae.
Phylogenetic analyses of three chloroplast regions (trnL-trnF spacer, trnL intron, and trnD-trnE spacer) provided strong branch support for a Paleotropical clade, which was further divided into two subclades: a 3-ovule clade and a 6-ovule clade. Rinorea subsect. Verticillatae showed a moderately to highly supported sister relationship to the Asian species. Biogeographic analyses confirmed at least five dispersals between Africa and Madagascar, and one between Madagascar and Asia.
The rate of endemism for Malagasy Rinorea is in excess of 90%. Phylogenetic and biogeographic analyses reveal that ca. 37% of species have affinities to African relatives and the remaining 63% (i.e., subsect. Verticillatae) are more closely related to Asian species. Several species are critically endangered or presumed extinct, while others are represented by substantial populations in protected areas.