11. Lathyrus palustris Linnaeus, Sp. Pl. 2: 753. 1753.
欧山黧豆 ou shan li dou
Herbs perennial, 15-100 cm tall. Stem climbing, branched, pubescent or glabrous, winged or unwinged. Leaves with simple or branched tendril at apex; stipules semisagittate, 12-25(-30) × 2-10 mm; leaflets 2-4-paired, linear to broadly lanceolate, without reflexed basal spur, 30-60 × 4-10(-15) mm, pubescent, veins pinnate or subparallel, abaxially prominent. Raceme longer than leaf, (2 or)3- or 4(-10)-flowered. Calyx campanulate, unequally toothed; longest tooth equaling tube. Corolla purple, 13-15(-20) mm; standard obovate, with claw; wings shorter than standard, obovate and longer than keels. Ovary linear. Legume linear, 3-4 cm, beaked at apex. Fl. and fr. Jul-Sep.
Marshes, wet meadows, a weed of rice fields; sea level to 3500 m. Gansu, Hebei, Heilongjiang, Hubei, Jiangsu, Jilin, Liaoning, Nei Mongol, Qinghai, Shanxi, Sichuan, Xinjiang, Xizang, Yunnan, Zhejiang [Japan, Korea, Mongolia, Russia; Europe, North America].
Lathyrus palustris is widely distributed in the N temperate zone in Europe, Russia, E Asia, and North America. It is a highly variable taxon with many entities described from it, although few of these stand up to scrutiny. East Asian specimens are often referred to L. palustris subsp. pilosus, but this is based purely on pubescence, a character with no other correlates. Consequently, we treat pubescent individuals at the varietal level. This species is often confused with L. quinquenervius. See under that species for the distinguishing characters.