© 2018 Magnolia Press. Aristida tovariana sp. nov. is described and illustrated. The new species, from southern Ayacucho, differs from A. achalensis in having spikelets 1–1.5 cm long, lemmas 5–6 mm long with awns 5.8–10 mm long, a twisted column not greater than 3 mm long, and fusiform caryopses with a ventral groove. A key to the species Aristida in Peru is included and the conservation status of the new species is evaluated.