Grossera (Euphorbiaceae) is a genus with eight species of trees and shrubs, seven of them from West and Central Tropical Africa and one from Madagascar. It occurs in a wide range of habitats, from primary to degraded forest, and from sea level to 1,350 m. Grossera is characterized by unisexual flowers, terminal inflorescences, anthers inserted on an androphore surrounded by five fleshy glands, three styles divided into two branches, ovary globose inserted in a plane disc thickened at the edge, and fruits in capsule with three 2-valved cocci. Although some regional treatments and a synopsis are available, a comprehensive monograph of the genus is lacking. In addition to a comprehensive key and descriptions, illustrations of five species and distribution maps for all species are provided here for the first time. Taxonomic discussions of each species have been included and three lectotypes are designated. Grossera major, synonymized by some authors, is clearly distinguished from G. paniculata because of its longer pedicels on male and female flowers. The eight accepted species (G. elongata, G. glomeratospicata, G. macrantha, G. major, G. multinervis, G. paniculata, G. perrieri, and G. vignei) are divided into three sections, including a new combination, Grossera sect. Columnella.