Ruellia saccata Schmidt-Lebuhn & E. Tripp, a new species of Acanthaceae from Beni, Bolivia, with a highly distinctive corolla morphology, is described as new to science. The novelty resembles and is related to R. brevifolia (Pohl) C. Ezcurra, but differs in the presence of a pronounced corolla pouch, a longer corolla with a narrower orifice, and a spreading to procumbent habit. Its differences from and similarities to other species in the genus are also discussed, and an updated key to the red-flowered Bolivian species of Ruellia L. is presented.