Taxonomic Studies on Malagasy Dalbergia (Fabaceae). IV. A New Species from Central and Southern Madagascar and a Narrowed Circumscription for D. emirnensis
Dalbergia emirnensis Benth. was previously treated as comprising two entities, the typical variety from the Central Highlands of Madagascar and D. emirnensis var. decaryi Bosser & R. Rabev. from the southern part of the country at lower altitudes. Additional collections and analyses demonstrate that, as currently delimited, these taxa exhibit considerable, discontinuous variability in morphology, habitat, and distribution, a finding supported by a recent phylogenomic study. We show that the material previously included in the typical variety of D. emirnensis represents two morphologically and geographically distinct entities, one that occurs only in the Central Highlands of Madagascar and includes the type specimen, and another that is morphologically and genetically more akin to D. emirnensis var. decaryi, found in the Southern Highlands of Madagascar. We describe the latter as a new species, D. nemoralis Rakoton., Phillipson & Crameri, in which we include D. emirnensis var. decaryi, recognizing it as a distinct subspecies. We also show that D. campenonii Drake should be treated as a synonym of D. emirnensis. Each of the accepted taxa is provided with a full description, a comprehensive listing of specimens examined, details of its geographic distribution and habitat, and a provisional risk of extinction assessment using the IUCN Red List categories and criteria; a line drawing is also provided for D. nemoralis subsp. nemoralis.