Description from Flora of China
Gerardia japonica Thunberg in Murray, Syst. Veg. ed 14, 553. 1784; Phtheirospermum chinense Bunge.
Annuals, (5-)60-100 cm tall. Stems erect or curved and ascending, usually much branched. Leaves opposite; petiole 5-12 mm, narrowly winged; leaf blade narrowly triangular-ovate, 1.5-5.5 X 0.8-3 cm, pinnately parted to pinnatisect; pinnae narrowly ovate to ovate-orbicular, 4-10 X 2-5 mm, base suboblique, margin double serrate or parted. Pedicel 2-7 mm. Calyx 4-10 mm; lobes lanceolate, 2-6 X 1-3 mm, foliaceous, pinnately parted. Corolla pale red to purple-red, 0.8-2.5 cm, outside villous; lower lobes obtuse; upper lobes triangular-ovate. Filaments basally pilose. Capsule 6-10 mm. Seeds flattened, ca. 1.2 mm. Fl. and fr. Jun-Oct.
Shady places in thickets on mountain slopes; 100-1900 m. throughout China except Xinjiang [Japan, Korea, Russia (Far East)].