Résumé
Background: Tropical forests are renowned for hosting a remarkable diversity, but the estimation of their species richness depends on the species concept used for their delimitation. Hence, species richness can be underestimated by the occurrence of cryptic species or overestimated by taxonomical oversplitting. Phylogenetic approaches are increasingly used to help decipher species delimitation. However, reciprocal monophyly at gene trees requires that the number of generations since speciation largely exceeds the effective population sizes of the sister species. Alternatively, population genetics methods allow to assess reproductive isolation, which is at the basis of the biological species concept. Using the latter species concept, we relied on large-scale genotyping using nuclear microsatellite markers to evaluate species delimitation in several African tree taxa. To this end, we considered that distinct species can be recognized when well differentiated genetic clusters occur in sympatry. Results: ( i ) We found no case of oversplitting: even when phenotypically very similar, species distinguished by taxonomists formed distinct genetic clusters, although hybridization was occasionally detected. ( ii ) By contrast, in nearly half of the taxonomical species investigated, we found several sympatric genetic clusters, indicating that cryptic species are not uncommon. ( iii ) Interestingly, a re-examination of morphological traits associated to each genetic cluster can reveal diagnostic characters, so that taxonomy can greatly benefit from population genetics approaches to resolve species complexes. ( iv ) Finally, we found that markers from the chloroplast genome were not always reliable to distinguish closely related species, limiting the usefulness of plastid- based DNA barcodes. Significance: According to our results the number of African tropical tree species might in reality be underestimated by a two-fold factor due to (near) cryptic species.