Description from Flora of China
Alisma plantago-aquatica Linnaeus var. orientale Samuelsson, Acta Horti Gothob. 2: 84. 1926; A. plantago-aquatica subsp. orientale (Samuelsson) Samuelsson.
Tubers 1-2 cm in diam. Aerial leaves with petiole 3-34 cm; leaf blade broadly lanceolate to elliptic, 3.5-11 × 1.3-7 cm, sometimes larger, 5-7-veined, base rounded or subcordate, apex acuminate. Panicles 20-70 cm, in 3-9 whorls of 3-9 branches. Pedicel 0.5-2.5 cm. Sepals ovate, 2-2.5 × ca. 1.5 mm. Petals white or pinkish, suborbicular, larger than sepals, margin undulate. Anthers ca. 0.5 × 0.3-0.4 mm. Carpels irregularly arranged; styles erect, ca. 0.5 mm, longer than ovary, stigmatose in upper ca. 1/5 of their length. Achenes elliptic, 1.5-2 × ca. 1 mm, 1- or 2-grooved abaxially; lateral pericarp usually opaque, thickish. Fl. and fr. May-Sep. 2n = 28*.
This species is similar to Alisma plantago-aquatica but differs in having flowers and fruit smaller, styles only ca. 0.5 mm, and petal margins and carpels irregularly arranged.
Margins of lakes, ponds, marshes, channels; below 2500 m. Anhui, Fujian, Gansu, Guangdong, Guangxi, Guizhou, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Jilin, Liaoning, Nei Mongol, Ningxia, Qinghai, Shaanxi, Shandong, Shanxi, Sichuan, Xinjiang, Yunnan, Zhejiang [India, Japan, Kashmir, Korea, Mongolia, Myanmar, Nepal, Russia, Vietnam].