Description from Flora of China
Herbs, perennial, less robust than L. salicaria, 50-100 cm tall, glabrous throughout. Stem erect, 4-angled. Leaves opposite, sometimes alternate, narrowly lanceolate to linear-lanceolate, 3-13 × 0.3-1.6 cm, base narrowly cuneate, apex acute-acuminate. Inflorescences terminal, spicate, 13-25 cm; bracts linear-lanceolate. Flowers in 1-3(-7)-flowered axillary cymes, solitary or in sparse whorls, shortly pedicellate. Floral tube 4-6 × 1-1.5 mm, 12-ribbed; sepals deltate, 0.8-1 mm; epicalyx segments erect, linear to awl-shaped, shorter than or equaling sepals. Petals purple to pink, elliptic-lanceolate or oblanceolate, 5.5-7 × 2.5-4 mm. Fl. Apr-Aug, fr. Jul-Sep. 2n = 30, 40.
Damp places. Hebei, Xinjiang [E Europe to SE Siberia].