Generic delimitations within the Rottboelliastrae Stapf and Coelorachidastrae Clayton (formal name) are revised. Coelorachis Brongn., Hackelochloa O. Ktze, Heteropholis C.E. Hubb., Ratzeburgia Kunth, and Rottboellia formosa R. Br, are to be included in Mnesithea Kunth. Heteropholis cochinchinensis (Lour.) Clayton and its variety chenii (Hsu) Sosef & Koning are varieties of Mnesithea laevis (Retz.) Kunth. Robynsiochloa Jacq.-Félix is to be included in Rottboellia L. f. The necessary new combinations, a list of genera and representative species, and a key to the genera are given. In the Appendix a new species of Rottboellia, R. paradoxa Koning & Sosef, is described from the Philippines. The enigmatic species Rottboellia villosa Poir. is transferred to Schizachyrium villosum (Poir.) Veldk., comb. nov.