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.
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Perennials to 1 m tall. Stems erect, 4-angled, 2-sulcate. Petiole (0-)3-5 mm, sulcate, hispid; leaf blade elliptic, obovate, or oblong, 2-9 × 1-3 cm, with numerous cystoliths, both surfaces densely strigose, secondary veins 8-15 on each side of midvein and abaxially prominent, base decurrent onto petiole, margin entire or slightly undulate, apex acute to obtuse. Flowers several clustered in leaf axils, sessile; bracteoles linear-oblong, ca. 6 mm, densely hispid-ciliate. Calyx ca. 1.1 cm, 5-lobed to middle; lobes linear-lanceolate, densely white hispid-ciliate. Corolla purplish blue, 1.8-2.2 cm, pilose; tube basally cylindric for ca. 5 mm and ca. 2 mm wide then gradually widened to ca. 6 mm at mouth; limb 2-lipped; lower lip oblong, 3-lobed, lobes ovate and ca. 2 × 2 mm; upper lip triangular, 2-lobed. Stamens 4; filaments glabrous, longer pair ca. 6 mm, shorter pair ca. 3 mm; anther thecae ca. 2 mm. Ovary glabrous; style pilose. Capsule 1.2-1.5 cm. Seeds blackish brown, ca. 1.5 × 1 mm, pubescent.
A herb. It keeps growing from year to year. It grows 1 m tall. The stems are erect and 4 angled. The leaves are oval and 2-9 cm long by 1-3 cm wide. The edges can be slightly wavy. The flowers are in clusters in the axils of leaves. They are purplish-blue.
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