Unraveling the complex systematics of Malagasy Donella species (Sapotaceae) using herbarium phylogenomics

Donella is a genus of tropical trees distributed across Africa and Madagascar with a single species in Asia. While a recent taxonomic revision provided a genus-wide morphological framework, the circumscription of the Malagasy taxa remained difficult, hindering conservation assessments in this high-diversity region. We employed a phylogenomic framework to delimit species boundaries and infer evolutionary relationships within the Donella lineage. A set of 99 specimens, selected to capture the breadth of morphological and geographic variation of the Malagasy species from ∼ 230 unique collection numbers, was analysed using a target enrichment approach. We inferred phylogenetic relationships on nearly 800 nuclear loci using both species-tree and network analyses, assessed genome-wide heterozygosity levels, and implemented species delimitation models as well as niche modelling. All Malagasy taxa, except Donella guereliana, form a clade, characterized by a radiation-like topology. Results across analytical approaches are largely congruent and agree with morphological differentiation and geographic structuring. Donella lanceolata, previously thought to occur in Madagascar, is resolved as sister to the Malagasy clade, with the Malagasy specimens representing a distinct species, here recognized as D. malagassica comb. et stat. nov. Two species are newly described, D. ricardorum sp. nov. and D. cryptica sp. nov.; D. sambiranensis is reinstated; D. humbertii is synonymized under D. analalavensis; and D. guereliana is excluded from the genus. The taxonomic changes proposed here refine the circumscription of the genus Donella and its Malagasy species, while demonstrating that 73% of the species in Madagascar are threatened according to IUCN criteria, highlighting the urgent need of targeted conservation measures.