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 morphological revision resolved several taxonomic ambiguities, the circumscription of Malagasy taxa remained problematic, 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 from ~230 unique collection numbers, was analysed using target sequence capture with Illumina sequencing. We generated a species tree and a phylogenetic network, conducted principal component analyses (PCA), assessed genome-wide heterozygosity levels, and implemented species delimitation models.All Malagasy taxa, except Donella guereliana, form a monophyletic 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.This taxonomic revision refines the circumscription of the genus Donella and of its Malagasy species while demonstrating that 73% of them are threatened under IUCN criteria, highlighting the urgency of targeted conservation measures.