Since its description, almost 100 years ago, the genus Dinizia has been treated as monospecific, comprising the single canopy-emergent species Dinizia excelsa Ducke which grows in non-flooded Amazonian forests of Guyana, Suriname and seven states of northern and central-western Brazil. Dinizia jueirana-facao G. P. Lewis & G. S. Siqueira, which grows in a restricted area of semi-deciduous Atlantic rain forest in Espírito Santo state, Brazil, is described as a new species in the genus. The new species is also a canopy-emergent of impressive stature. We provide descriptions for both species, a key to species identification, a distribution map and the new species is illustrated. Fossil leaves, inflorescences and fruit provide evidence for a Dinizia-like ancestor occurring in south-eastern North America during the Eocene. In contrast to D. excelsa where pollen is dispersed in tetrads, the pollen of D. jueirana-facao is shed in monads. D. jueirana-facao is considered critically endangered following IUCN conservation criteria, whereas D. excelsa is assessed to be of least concern. A lectotype is designated for D. excelsa.