A new genus and species of Euphorbiaceae s.s., Brasiliocroton mamoninha, is described from two disjunct areas of lowland forest remnants in eastern and northeastern Brazil. It is a member of tribe Crotoneae and was previously confused with Croton and Micrandra. The resemblance to Micrandra is based on the branched inflorescences and terminal position of the pistillate flowers, trigonous capsules, and ovate leaves with basal glands, but the stamens are more numerous and the pollen is inaperturate (like Croton). Brasiliocroton has a stellate-rosulate indumentum like some Croton species, but its anthers are erect in bud, and the position of the pistillate flowers is anomalous in Croton. Molecular data place Brasiliocroton as the closest sister group to Croton, once Astraea has been removed from Croton and placed sister to Acidocroton and Ophellantha. Wood anatomical features support the generic status of Brasiliocroton.