Herbs up to 30 cm. high or more; stems simple, subquadrangular, pilose, the hairs septate, spreading or ascending, about 0.5 mm. long; leaf blades oblong-elliptic, up to 11 cm. long and 3.5 cm. wide, more or less falcate-acuminate (the tip itself blunt), narrowed to rounded at base, moderately firm, entire or undulate, the upper surface gla- brous, minutely alveolate under lens, the cystoliths numerous, con- spicuous under lens, 175μ long, the lower surface moderately hirtel- lous, the hairs ascending or appressed, confined chiefly to costa and veins (6 to 7 pairs), these more prominent than above, the veinlets rather prominently and coarsely reticulate; petioles 1.5 cm. long, hirtellous with brownish, curved hairs; flowers arranged in fascicles of usually 2 to 8 flowers each, forming sparingly branched terminal panicles up to 7 cm. long, the peduncles up to 5.5 cm. long, the lower-most internode 2.5 cm. long, the others successively shorter toward tip, both peduncle and rachis hirtellous, the hairs ascending, up to 0.5 mm. long, septate; bracts subtending the lowermost branches of the inflorescence linear to narrowly lanceolate, leaflike, 1 to 2 cm. long, 1 to 6 mm. wide; bracts subtending the fascicles narrowly lanceolate, up to 3 mm. long, about 1 mm. wide at base, acute, glabrous or sparingly hirtellous and ciliolate; bractlets similar to the bracts, but slightly smaller; pedicels slender, up to 3 mm. long, 0.25 mm. in diameter, puberulous; calyx segments narrowly lanceolate, about 3 mm, long and 0.5 mm. wide, acute, sparingly puberulous; corolla 12 mm. long, white tinged with blue (Pennell), puberulous or the lobes glabrous toward margins, the tube narrow, 1.25 mm. broad near base, narrowed at 1.5 mm. above base to 0.75 mm., thence abruptly enlarged from about the middle to 1.5 mm., the limb 8 mm. broad, the lobes ovate, 5 mm. long, subobtuse or rounded; stamens attached at middle of tube, 2 mm. long, the anthers 1.5 mm. long, 0.5 mm. broad, the staminodes 0.5 mm. long; ovary puberulous, mature capsules not seen. Type in the herbarium of the New York Botanical Garden, collected at edge of forest about Antizales, Department of Bolívar, Colombia, 1,500-1,800 meters altitude, February 25 or 26, 1918, by Francis W. Pennell (No. 4436). Pseuderanthemum stenosiphon can be recognized among its close relatives by the bluish flowers with very narrow corolla tubes. Hence the specific epithet, σrevós, slender, and wiper, tube.