Generic delimitation of Turraea (Meliaceae–Turraeeae) and allied genera in continental Africa and Madagascar

Abstract We investigated here speciation and diversification mechanisms in Turraea and allied genera (Meliaceae-Turraeeae) from Madagascar and continental Africa, as well as their generic delimitations. Our goal was to contribute to an improved understanding of the origin and diversification of the Malagasy and African floras. Using target-enrichment sequencing, we assembled a nuclear dataset comprising 64 taxa (75% of the group’s species diversity) to reconstruct phylogenetic relationships within the group. We estimated divergence times and diversification rate shifts and assessed the prevalence of incomplete lineage sorting and introgression/hybridization. The group appears to have originated in the Eocene, probably in southern Africa, with a diversification rate shift occurring in the Miocene coinciding with the colonization of Madagascar. This shift, associated with incomplete lineage sorting and introgression/hybridization, suggests a rapid diversification linked to the onset of the Indian Monsoon. We propose a revised generic classification, including a new key and synoptic descriptions of the genera, to accommodate the polyphyly of Turraea. In this context, we place the endemic Malagasy genera Humbertioturraea and Calodecaryia in synonymy under Turraea, and resurrect the South African genus Nurmonia and the Angolan and Indian genus Naregamia. We therefore publish the necessary new combinations in Nurmonia and Turraea.