Herbs; stems erect or ascending, 20 to 30 cm. high, subquadrangu- lar, glabrous below, pilose above, the hairs 1.5 mm. long; leaf blades oblong-elliptic, 2 to 8 cm, long, 1 to 3.5 cm. wide, obtuse or rounded at apex, sometimes bluntly acuminate, narrowed at base, glabrous, the cystoliths numerous; petioles up to 2 cm. long, glabrous or spar- ingly pilose; flowers borne in terminal bracted spikes up to 3 cm. long; bracts imbricate, lanceolate, about 15 mm. long and 6 mm. wide, ob- tuse at apex, pilose and strongly ciliate; bractlets linear, 13 mm. long, 1.5 mm. wide, pilose; calyx 8 mm. long, the tube glabrous, the seg- ments lanceolate, 7 mm. long, 1.5 mm. wide near base, ciliate; corolla about 2.5 cm. long, purple, minutely pubescent, the tube hypocra- teriform, the lower half slender, the upper half campanulate, about 6 mm. broad at throat, the limb 10 to 12 mm. broad, the lobes ovate; capsules 8 mm. long, about 3 mm. wide, clavate, glabrous, the solid basal portion about 1 mm. long, 6-seeded; seeds flat, reddish brown, suborbicular, 2 mm. long and 2.5 mm. broad, glabrous when dry, very finely mucilaginous-pilose when moistened; retinacula 1.5 mm. long, subulate, curved, truncate and lacerate at tip. Type in the U. S. National Herbarium, collected in frequently sub- merged areas in the San Juan Valley (Camp VI), Department of Santander, Colombia, 100 to 700 meters altitude, June 9, 1935, by Oscar Haught (No. 1762). Haught's No. 1496a, collected at Camp Mesa, vicinity of Barranca Bermeja, Magdalena Valley, between the Sogamoso and Colorado Rivers, Santander, 100 to 500 meters altitude, also represents the species. Ruellia aquatica is unlike any other Colombian Ruellia hitherto described. The name aquatica alludes to the habitat of the species.