Description from Flora of China
Urtica dioica var. angustifolia (Fischer ex Hornemann) Ledebour; U. foliosa Blume.
Herbs perennial, dioecious. Rhizomes woody, stoloniferous. Stems branched or simple, 40-150 cm tall; stems, petioles, and both surfaces of leaf blade sparsely hirtellous and armed with stinging hairs. Stipules free, linear, 6-12 mm; petiole short, 0.5-2 cm; leaf blade oblong-lanceolate to ovate-lanceolate, rarely linear or ovate, 4-15 × 1-3.5(-5.5) cm, often herbaceous, 3-veined, lateral basal veins parallel to midvein in middle of blade, with secondary veins 2 or 3 on each side, adaxial surface often rough, base rounded, rarely shallowly cordate, margin coarsely 9-15(-19)-dentate or serrate, teeth tapered or incurved-tipped, ciliate, apex long acuminate or acute; cystoliths often punctiform. Inflorescences paniculate, sometimes with few, short branchlike spikes, 2-8 cm. Male flowers in bud ca. 2 mm, perianth lobes connate 1/2 of length, puberulent. Female flowers: perianth lobes connate at base, dorsal-ventral lobes elliptic-ovate, ca. 1 mm, sparsely setulose or subglabrous, lateral lobes narrowly obovate, 1/2 the length of dorsal ones. Achene brownish gray, ovoid or broadly ovoid, slightly compressed, 0.8-1 mm, smooth or inconspicuously verrucose, invested by persistent perianth lobes. Fl. Jun-Aug, fr. Aug-Oct.
The species is similar to Urtica dioica in having dioecious plants, paniculate inflorescences, and similar stipule and achene features; however, it differs in having sparser stinging hairs, narrower leaves with a rounded base, and much shorter petioles. The taxa could either be sister species, or U. angustifolia could be an eastern geographical vicariant of U. dioica.
Moist places in forests, thickets, stream banks; 800-2200 m. Hebei, Heilongjiang, Jilin, Liaoning, Nei Mongol, Shandong, Shanxi [Japan, Korea, Mongolia, Russia (Far East, Siberia)].