Herbs 20-50 cm tall, isophyllous. Stems slender, herbaceous, much branched; branchlets purplish red, 4-angled then terete, glabrous. Petiole 2-5 cm, white pubescent; leaf blade narrowly elliptic to lanceolate, 2-5 × 0.5-1.8 cm, both surfaces glabrous and densely covered with prominent linear cystoliths, secondary veins 3-5 on each side of midvein, base cuneate to broadly cuneate, margin crenulate, apex long acuminate. Inflorescences terminal, spikes, 1-3(-5) cm, sometimes reduced to a single flower pair; bracts imbricate, oblanceolate to oblong-lanceolate, 7-10 × 2-3 mm, as long as corolla tube, glabrous except for pubescence at base, apically densely covered with cystoliths, margin entire, apex obtuse; bracteoles linear, ca. 5 mm. Calyx equally 5-lobed almost to base; lobes linear, 6-7 mm, margin ciliate, apex rounded. Corolla purplish white or white, funnel-shaped, ca. 1.5 cm, straight, outside pubescent, inside glabrous except for trichomes retaining style; tube basally cylindric for 5-6 mm; lobes oblong-elliptic, 5-6 mm, equal. Stamens 4, included; shorter filament pair ca. 8 mm; longer filament pair ca. 1.2 cm; anther thecae oblong, ca. 1.5 mm; pollen type 10. Ovary glabrous; style filiform, ca. 1.2 cm, pilose; stigma 2-cleft. Capsule oblong, ca. 7 mm, presumably glabrous, 4-seeded. Seeds ovate in outline, ca. 3 mm, densely appressed pubescent. Fl. Aug-Sep, fr. Oct-Nov. 2n = 30.
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