Systematics and biogeography of Oleaceae subtribe Schreberinae, with recircumscription and revision of the Malagasy members

Abstract

Abstract Clarifying generic circumscriptions in Oleaceae improves its complicated infrafamilial classification. Focusing on the small and disjunctly distributed subtribe Schreberinae, we use phylogenomic data from plastid and nuclear DNA from an extensive sampling to assess its phylogenetic patterns and biogeographic history. Results show paraphyly in the subtribe, with Comoranthus nested in Schrebera, leading us to synonymize these genera. Schrebera s.l. occurs in four major regions of the world, but its centre of origin remains uncertain, with three possible ancestral ranges identified. However, the diversification of this genus is estimated to have started in the Early Oligocene (c. 34 Mya), and its current distribution pattern is best explained by dispersal between landmasses rather than continental vicariance. Madagascar is the centre of diversity of Schrebera s.l., where ten endemic species, of which five are new, were recovered from analyses of morphological, molecular and ecoclimatic data. Therefore, a taxonomic treatment of the species from Madagascar and the Comoro Islands is presented. As currently circumscribed, Schrebera s.l., and thus the monogeneric subtribe, includes 16 species (one in South America, two in Southeast Asia, three in Africa, of which one is shared with Madagascar, and 11 in Madagascar and the Comoro Islands).