Suffrutescent herb up to 5 meters high; stems quadrangular (the angles rounded), up to 2 cm. in diameter, glabrous, verrucose at nodes; leaf blades lanceolate to rhombic, up to 30 cm. long and 17 cm. wide, acuminate or acute, acute at base and decurrent on the petiole, crenate, rather thin, glabrous above, the cystoliths conspicuous under a lens, the costa and lateral veins (8 to 10 pairs) finely appressed pubescent; petioles 1 to 2 cm. long; flowers numerous, clustered in the axils of the upper leaves; calyx up to 7 mm. long, the segments lanceolate, acuminate, 6 mm. long and 2 mm. wide, glabrous below, sparingly pilosulose toward tip of segments; corolla 3 to 3.5 cm. long, pale green, sparingly puberulous, the tube hypocrateriform, the lower half slen- der, about 1.5 mm. in diameter, the upper half narrowly campanulate, about 8 mm. in diameter at mouth, 1.5 to 2 cm. broad, the lobes ovate; stamens included; capsule 17 mm. long, 4 mm. broad, clavate, the solid basal portions slender, comprising about one-half the length of the capsule, glabrous, 6-seeded; retinacula 2 mm. long. Type in the Herbarium of the Riksmuseet, Stockholm, collected in thick forest 130 miles north of Bogotá at "El Humbo," Department of Boyacá, Colombia, "2500 feet" altitude, September 30, 1932, by A. E. Lawrance (No. 491). Isotypes are in the Gray Herbarium and the herbaria of the Missouri and New York Botanical Gardens. A type fragment is in the U. S. National Herbarium, No. 59583.
Ruellia viridiflora is a well-marked species, easily recognized by its large size, large crenate leaves, and axillary clusters of pale green flowers.