Erect to spreading, aquatic, to subaquatic herb, 40-100 cm tall. Younger stem quadrate-sulcate to hexagonal-ridged, glabrous, older stem subquadrangular, glabrescent, inconspicuously lenticellate. Petiole 0.5-1 cm long, glabrate or sparingly pilose; blade narrowly oblong-obovate to oblanceolate, 2.5-7 x 1.8-4 cm, apex obtuse or rotundate, base attenuate and decurrent on petiole,both surfaces moderately pilose, margin entire, cystoliths difficult to detect; secondary veins 5-6 pairs. Inflorescence of opposite or alternate dichasia, 1-3 flowered; peduncle to 1 mm long; bracts subtending lateral flowers oblong-lanceolate, 5-14 x 6-8 mm, moderately pilose, margin ciliolate; bracteoles narrowly oblong, 6 x 3 mm, moderately pilose, margin ciliolate. Flowers sessile to subsessile; calyx 11-14 mm long, 5 equal lobes basally fused for about one-half, lobes narrowly linear-lanceolate, purplish, apically subcaudate-acuminate, sparingly hirsute, cystoliths numerous and conspicuous, margin sparingly ciliolate; corolla reddish, 17-20 mm long, sparingly and minutely pubescent without, lower half of tube cylindrical, 5-7 mm long, upper half enlarged, upper lip erect, 2-lobed, 9-10 mm long, lobes retuse, 1.5 x 1.5 mm, lower lip 3-lobed, 8-9 mm long, lobes oblong-lanceolate, 2-2.5 x 1.5 mm; stamens inserted near base of throat, longer pair 7 mm long, shorter pair 3.5-4 mm long, anthers 2 mm long, purplish; ovary glabrous, 3 mm high, style 14 mm long, basally glandular-pubescent. Capsule narrowly oblong, 13-14 x 2 x1.8-2 mm, glabrous, glossy, obtuse and apiculate, retinacula 0.5-0.8 mm long; seeds 12-18, flattened, brown, irregularly orbicular, 1.2 x 1 mm.
Asia present, Malaysia present, rice fields in Suriname
Introduced from Asia and Malaysia into rice fields in Suriname (SU: 13).