Simple erect herbs up to 60 cm. high; stems subquadrangular, glabrous or the upper portions hirtellous in 2 lines, the cystoliths par- allel, 250 long; leaves crowded at the tip of stem, the blades ovate, up to 14 cm. long and 8 cm. wide, short-acuminate (the tip itself blunt), abruptly narrowed into a slender, winged petiole, membrana- ceous, drying bright olive-green, entire, glabrous or sparingly hir- tellous, the hairs of the upper surface coarse, about 0.5 mm. long, those on the lower surface smaller and finer, confined chiefly to costa and lateral veins (usually 8 pairs), the venation of the upper surface ob- scure, that of the lower more prominent and drying a bright yellowish green, the cystoliths slender, inconspicuous, 250 μ long; petioles 4 to 10 cm. long, including the wings, about 10 mm. wide at base of blade, thence gradually narrowed to base; raceme terminal, simple, slender, the peduncle 12 cm. long, the lowermost internode 7 cm. long, the others successively shorter toward tip, both peduncle and rachis moderately hirtellous, the hairs mostly spreading, straight or curved, 0.25 mm. long, the pedicels up to 1 mm. long; bracts subtending the spike and lowermost branches of the inflorescence leaflike, suborbicular, obtuse, cordate, the lowermost pair about 4 cm. wide, the second pair 2 cm. wide, the upper flower bracts lanceolate, 4 mm. long or less, 0.75 mm. wide at base, acute, subcarinate, moderately ciliate, minutely hirtellous at tip, the margins subhyaline; bractlets narrowly lanceolate, 1.5 mm. long, 0.5 mm. wide, acute, sparingly and minutely hirtellous at tip, otherwise glabrous; calyx segments linear-lanceolate, 2.5 mm. long, 0.25 to 0.5 mm. wide at base, acuminate, minutely hirtel- lous and ciliolate at tip; corolla 2.5 cm. long, purple (morada), the tube slender, 0.75 mm. in diameter except at mouth, here 1.5 mm. broad, the limb spreading, the lobes oblong, 9 mm. long, up to 4.5 mm. wide, rounded or obtuse, the stamens slightly exserted; capsules not seen. Type in the U. S. National Herbarium, No. 2025691, collected on the margin of the Río Guejar, Sierra de La Macarena, Intendencia of Meta, Colombia, 500-1,000 meters altitude, August 29, 1950, by J. M. Idrobo (No. 536). Pseuderanthemum idroboi is closely related to the preceding species, differing chiefly in color of flower and in the shape of the flower bracts.