Annual, erect herb 40-300 mm high; stems simple or branching from base, lateral stems up to 100 mm long, square in cross-section, ridged because of decurrent leaf bases, often dark reddish, leafy. All parts of plant glandular pilose, except most of corolla, with spaced, transparent to whitish hairs, mostly ± patent, terete with exudate a little broader than hair itself. Leaves simple, opposite to subopposite or sometimes alternate near stem apex, sessile to shortly petiolate, decurrent on stem; leaves on short, lateral shoots tufted and appear congested and clumped together; lamina narrowly lanceolate, elliptical or oblong, often longer than internodes, 11-40 x 2-7 mm; base attenuate; apex mostly obtuse sometimes sub-obtuse, rarely acute; margins entire to sparingly dentate with 2-7 pairs of very small, narrowly deltoid teeth, usually in upper half. Bracts alternate, sessile, leaf-like, becoming smaller upwards. Pedicels up to 9 mm long, elongating and recurved or variously contorted when fruit matures. Calyx 5-lobed, spreading, 1.5-6.3 x 0.4-1.8 mm, weakly bilabiate with two lobes somewhat broader than the other three, oblanceolate to narrowly obovate or oblong; apex mostly obtuse some sub-obtuse, glandular pilose. Flowers axillary or in lax racemes up to 80 mm long. Corolla bilabiate, 3.8-8.3 x 1.9-6.5 mm, pale to bright yellow; upper lip 4-lobed, 3.9-5.1 x 2.4-3.8 mm, base a stronger yellow with faint magenta to maroon venation forming vertical streaks, continuing down into the tube, base ± perpendicular to margins, apex rounded to emarginate; two inner lobes slightly smaller than other two, semi-erect, oblong to ovate; two outer lobes oblong to elliptic, slightly spreading; lower lip with one lobe, widely obovate and emarginate or obcordate, 2.3-2.6 x 1.0-3.3 mm, basal portion inflated into convex projecting palate; palate bright yellow, longitudinally grooved, glabrous; boss glabrous or slightly papillate, a stronger yellow than main part of corolla; tube >0.5 mm long, pale yellow; hypocotyle (floor of corolla tube) 3.0-3.3 mm long, sides invaginated to form a narrow channel, base of tube drawn out into a conical, backward-projecting spur, 1.8-4.4 x 0.2-1.4 mm, glabrous, bright yellow, held ± parallel to the pedicel. Stamens 4, lying in a shallow depression in upper inside surface of corolla tube; filaments of anticous pair 1.1-1.8 mm long, sigmoid, ± straight in middle; posticous filaments 0.6-0.7 mm long, ± straight except at base; anthers 0.5-0.6 mm long, each pair strongly coherent. Ovary ovoid, 2.0-2.5 x 1.0-1.5 mm, glabrous, laterally compressed; style stout, straight, 0.4-0.5 x 0.3-0.4 mm, compressed contrary to the ovary, apex wider than base, lying between anther pairs; stigma simple, oval or slightly triangular in cross-section, stigmatic surface finely papillate, darker than style. Capsules ± oblong-ovoid in outline, 4.5-11.0 x 4.0-5.0 mm, laterally compressed contrary to septum, apex emarginate to bilobed, lobes rounded to acute with very steep angle between them, apical incision 1.0-2.3 mm deep. Seeds widely ovate, 1.2 x 0.3-1.7 mm, light brown, verruculate, winged; wing membranous and fluted. Flowering & fruiting: August-September.
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