Herbaceous or suffrutescent plants up to 1 meter high; stems ascending and rooting at the lower nodes, branched, subquadrangular, glabrous or minutely strigose, the hairs up to 0.16 mm. long, upwardly appressed, the nodes of the stem swollen, the internodes 1 to 5 cm. long, those of the lower part of the stem 5 mm. in diameter; leaf blades ovate to oblong-ovate, up to 9 cm. long and 2.5 cm. wide, the larger and lower blades slenderly acuminate at the tip, narrowed and decurrent on the petiole at base, the uppermost blades acute to short- acuminate (the tip itself subacute), rounded at base, all moderately firm, entire or undulate, the upper surface evenly appressed-hirsute, the hairs about 0.16 mm. long, the lower surface essentially glabrous, the costa and lateral veins (7 or 8 pairs) moderately conspicuous, appressed-hirsute, the hairs similar to those of the upper surface, the cystoliths inconspicuous or lacking; petioles slender, 1.5 cm. long (unwinged portion), appressed-hirsute; panicles axillary and terminal, becoming rather numerous, rigid but delicate, up to 5 cm. long and 2 to 4 cm. broad, the branches in pairs or solitary near the tip of the panicle, the peduncles slender, up to 3.5 cm. long and slightly over 0.25 mm. in diameter, the internodes of the panicle slender, up to 13 mm. long, hirtellous, the hairs ascending, about 0.16 mm. long, the lowermost branches subtended by small leaves, the others by small bracts, these narrowly triangular, 1.5 mm. long, barely 0.5 mm. wide at base, acute, sparingly hirtellous; calyx 8 mm. long, the segments narrowly linear, 7 mm. long and 0.5 mm. wide, faintly 3-nerved, acute, moderately hirtellous with sharply ascending rigid hairs up to 0.1 mm. long and sometimes also bearing a few slender spreading elongate-glandular trichomes about 0.5 mm. in length; corolla pale lavender, minutely puberulent, 12 to 15 mm. long, the upper lip 8 mm. long, linear, about 2 mm. wide at base, narrowed to a slender con- torted tip, the lower lip ovate, 5 mm. wide, 3-lobed at tip, the lobes about 1 mm. long and 0.5 to 0.75 mm. wide, obtuse at tip, stamens erect, exserted 10 mm. beyond the mouth of the corolla tube, the anthers 2 mm. long and 0.5 mm. wide, purplish, the filaments glabrous; style slightly exceeding the stamens, the stigma minute, subcapitate, the style glabrous; capsules clavate, flattened, 9 mm. long, 3 mm. broad and 1 mm. thick, glabrous; seed flat, suborbicular, about 2.25 mm. long and 2 mm. wide, white, minutely tuberculate.
Type in the U. S. National Herbarium, No. 2059037, collected on a steep, densely wooded slope of Quebrada Riocito, on the Hacienda San Luis, 6 km. northwest of Gramalote and 35 km. west of Cúcuta, Department of Norte de Santander, Colombia, 2,400 meters altitude, April 8, 1944, by R. F. Fosberg and N. C. Fassett (No. 21733).
Fosberg states in his label data that the Quebrada Riocito is on the headwaters of Río Peralonso and that the woods where his specimen was collected were rather dry, at least during the season of his visit, and that it was not a typical rain forest. Only one plant was seen.
The salient characters of Habracanthus syscius are the numerous, axillary, rather small, graceful but rigid panicles with their rather densely hirtellous rachises and pale lavender flowers, the slenderly petioled and tipped leaves, and the tumid, swollen jointed, ascending stems, glabrous below and minutely strigose toward tip. The specific epithet is from the Greek word abokos, meaning "in deep shade" in allusion to the habitat of the plant.