Euphorbia flaviana, a new species endemic to the State of Bahia in eastern Brazil, is described and illustrated. The new species belongs to Euphorbia [subgenus Chamaesyce] section Crossadenia and is morphologically most similar to Euphorbia teres, from which it differs having thinner, longer, numerous verticillate branches, and involucral glands without appendages. An artificial key to all nine members of Euphorbia section Crossadenia is provided, and Euphorbia crossadenia is lectotypified.