Euphorbia leistneri R.H. Archer, a new species from the northern Kaokoveld, Namibia, is described. E. leistneri is a succulent shrub, superficially similar to E. monteiri Hook.f., showing a close affinity with E. transvaalensis Schltf. , but it differs from that species in its thick succulent branches and segments, prominent tubercles and leaves terminal. E. leistneri is a rare species, at present recorded only from near the Epupa Falls in the Cunene River, which is threatened by a proposed hydroelectric scheme. Keywords: Euphorbia, Euphorbiaceae, Leistner, new species, taxonomy, Trichadenia.