Merostachys delicatula, a new species recorded thus far only from the montane Atlantic forest of southern Bahia, is described and illustrated here. Comments on its taxonomy, distribution, habitat, and phenology are presented. Among the narrow-leaved congeners occurring in Bahia, the new species is most similar to M. leptophylla. It is distinguished by having internodes glabrous to scabrous (vs. glabrous in M. leptophylla); internodes with an infranodal band of trichomes (vs. absent); culm leaf sheaths abaxially scabrous (vs. glabrous); upper glumes 1.2–2.1 mm wide (vs. 3.5–4 mm); anthecia dull (vs. shiny); lemmas 1.5–2.7 mm wide, abaxially pubescent (vs. ca. 4 mm, glabrous); and paleas 1.2–2.3 mm wide (vs. ca. 4 mm). We also provide an assessment of the conservation status of the new species and a geographic distribution map for both species.