Borreria kelleri (Spermacoceae, Rubiaceae), is described as a new species from northeastern Argentina and Paraguay. The new species is morphologically similar to B. quadrifaria due to the presence of densely and notable hairs in the angles of the stems and pantoporate pollen grains, but B. quadrifaria can be distinguished by its leaf blades narrowly elliptic or obovate up to 50 mm long, coriaceous, 1–5 glomerules per flowering branch and the bracts equal or barely longer than the diameter of the terminal glomerule. A complete description of the new species, including micromorphological features of flowers, fruits, seeds and pollen grains, illustration, distribution map, conservation status assessment and comparisons with morphologically related species is provided.