Macrothumia M. H. Alford is described as a new genus of Salicaceae based on Neosprucea kuhlmannii Sleumer from Brazil. The deciduous perianth, papillate leaf teeth, presence of receptacular disk glands, and analyses of plastid DNA data suggest that the new genus is more closely related to Ahernia Merrill and Pleuranthodendron L. O. Williams than to Banara Aublet or Neosprucea Sleumer. The monotypic genus Aphaerema Miers of Brazil and Argentina is transferred to Abatia Ruiz & Pavón, based on analyses of plastid DNA sequences and on the lack of morphological discontinuities between the genera. Because the name Abatia spicata (Turczaninow) Sleumer already exists, Abatia angeliana M. H. Alford is published as a replacement name for Aphaerema spicata Miers. A lectotype for Aphaerema spicata is also designated. The monotypic Hispaniolan genus Priamosia Urban, originally described as separate from Xylosma G. Forster based on its few stamens (four, instead of eight to numerous), is transferred to Xylosma, and a neotype is designated for Xylosma domingensis (Urban) M. H. Alford.