The uncommon southern African and Malagasy genus Sartidia in the Aristidoideae, Poaceae resembles the closely related Aristida but has a C-3 photosynthetic system, 3-5-veined lower glumes, and a ventrally grooved caryopsis. We present a revision of Sartidia in Madagascar with two species. Sartidia isaloensis is described as new based on its interrupted inflorescence structure, small spikelets, and short awns. A leaf anatomical study and a delta C-13 analysis confirm that S. isaloensis is a C-3 species. Sartidia perrieri is likely extinct in the wild. We present descriptions, typification, illustrations, distribution maps, an identification key, and IUCN conservation assessments. A key to the Aristidoideae in Madagascar is also included.