Notes on the genus Exostema (Rubiaceae), its limits and sectional subdivision

Abstract

Based on recent molecular work by Paudyal & al., the generic limits of the Neotropical woody genus Exostema are reassessed with a view of making them more compatible with traditional, morphology-based generic concepts. A wide circumscription is favoured, congruent with Paudyal & al.'s “clade B” (the Exostema-Solenandra-Coutarea-Hintonia group). Thus defined, Exostema is a genus with 40 species and five natural sections and incorporates three generic splits that were proposed by Paudyal & al. To minimise nomenclatural disruption, a proposal to conserve the name Exostema Rich. against Coutarea Aubl. has been presented separately. Two new combinations at sectional rank are proposed.