Suffrutescent plants up to 1.15 meters high or more; stems ascend- ing, mostly simple, subquadrangular, hirtellous, the hairs brownish, about 0.28 mm. long, retrorsely curved, the lower portions of the stems subterete, glabrate or sparingly and retrorsely puberulous, the horizontal portions rooting at the nodes; leaf blades oblong-ovate or oblong-elliptic, 14 cm. long, 5.5 cm. wide, short-acuminate (the tip itself obtuse or rounded), obtuse or rounded at base, rather firm, entire, both surfaces glabrous or sparingly hirsute, the hairs brownish, up to 1.5 mm. long, ascending or subappressed, up to 1.5 mm. long, those of costa and lateral veins (10 to 12 pairs) smaller, up to 0.5 mm. long, the venation prominent beneath, less so above, the cysto- liths numerous and conspicuous, up to 0.25 mm. long; petioles stout, 2 to 4 mm. long, hirtellous with brownish ascending hairs up to 0.2 mm. long; spikes terminal, single or forked, up to 12 cm. long, the secondary peduncles about 2.5 cm. long, the lowermost internode of the rachis 1.5 cm. long, the others successively shorter toward tip of spike, these and the peduncles rather densely hirtellous, the hairs brown, more or less spreading, up to 0.3 mm. long; bracts subtend- ing spikes subulate, 4 or 5 mm. long, about 1 mm. wide at base, gradually narrowed to a blunt tip, subcarinate, firm, hirtellous like the rachis; bracts subtending the flowers subulate, the lowermost pair linear-lanceolate, 3.5 mm. long, 0.75 mm. wide, blunt at tip, striate, hirtellous, the others successively smaller toward tip of spike; bractlets
linear, up to 3.5 mm. long and 0.5 mm. wide, blunt at tip, hirtellous; calyx 6 mm. long, the segments narrowly lanceolate, 5 mm. long, 0.5 mm. wide near the base, gradually narrowed to an acute tip, sparingly hirtellous with spreading or ascending hairs up to 0.5 mm. long, delicately 3-nerved; corolla 13 mm. long, white with mauve markings on lip, rather sparingly puberulous, the hairs spreading, up to 0.13 mm. long, the lips subequal, 6 mm. long, the upper one oblong-ovate, about 3 mm. wide, rounded at tip, the lower one cuneate, 7 mm. wide at base of the 3 lobes, these ovate, 3 mm. long, the middle one 3 mm. wide at base, the lateral ones 2 mm. wide, all rounded at tip; stamens slightly exserted, the anthers 2 mm. long, dorsally pubescent, the cells vertical or slightly oblique at maturity, superposed, 1 mm. long, 0.5 mm. wide, the lower one calcarate, the tail 0.5 mm. long, cucullate and rounded at tip, the connective spurred, the filaments glabrous except at base, here retrorsely hirtellous with straight rigid hairs up to 0.24 mm. long; capsules 4-seeded, clavate, 1 cm. long, 2 mm. broad, 1.5 mm. thick, rather sparingly hirtellous, the hairs more or less spreading, up to 0.11 mm. long or a few at the tip of the capsule reaching 0.18 mm. in length, the acute hairs intermixed with shorter gland-tipped ones; retinacula curved or bent at middle, 1.5 mm. long, the tip rounded, thin, obscurely erose; seeds flat, about 2 mm. in diameter, light brown, obscurely tuberculate.
Type in the Kew Herbarium, collected on rocks in narrow gorge near stream, Gorgona Island (off coast of Cauca), Colombia, "200 ft." altitude, October 18, 1924, by C. L. Collenette (No. 614).
Justicia petraea may be related to J. sterea, a species with a similar inflorescence but with the leaf blades acute at base and the petioles longer. The specific epithet is from the Greek Terpaios, meaning living on or among rocks, in allusion to its habitat.