A new species of Euphorbia sect. Alectoroctonum from Brazil is described and illustrated. Euphorbia sarcoceras belongs to the “Dichlium” group, and is compared to Euphorbia estevesii, E. jablonskii, E. insulana, and E. sciadophila, the other species of E. sect. Alectoroctonum that also occur in Brazil. The new species occurs in seashore plains vegetation (“restingas”) in the states of Rio de Janeiro and Santa Catarina and is characterized by fleshy appendages of the cyathial glands. Problems concerning the application of the name Euphorbia laevigata are discussed, and a key to the species of E. sect. Alectoroctonum in Brazil is also presented.