Description from Flora of China
Sium erectum Hudson, Fl. Angl. 103. 1762; Berula angustifolia Mertens & W. D. J. Koch, nom. illeg. superfl.; Siella erecta (Hudson) Pimenov; Sium angustifolium Linnaeus, nom. illeg. superfl.
Plants 40–50(–100) cm. Stem hollow, branched, rooting at basal nodes. Submerged leaves 3–4-pinnate; ultimate segments linear. Aerial leaves 1-pinnate; pinnae 4–9(–15) pairs, basal pairs remote, sessile, ovate-lanceolate or oblong, 1.5–5(–7) ×
0.8–2.5(–3) cm, base obliquely truncate, usually with 1 lobe at basal edge, margins serrate or irregularly incised. Upper leaves smaller, sheaths expanded. Umbels 4–6 cm across; bracts 3–6, oblong or lanceolate, 6–21 mm, entire or incised; rays 5–15 (–20), 2–3 cm, unequal; bracteoles 5–8, 1.5–5 mm, unequal, usually entire, nearly as long as or longer than the pedicels; umbellules 10–20-flowered; pedicels 2–5 mm, unequal. Calyx teeth 0.4–0.8 mm. Fruit 2–2.2 × 1.5–2 mm. Fl. May–Jun, fr. Jul–Aug.
Streamsides, other riparian habitats on plains or hills; ca. 1500 m. Xinjiang [Afghanistan, NW India, Kashmir, Kazakhstan, Kyrgyzstan, W Nepal, Pakistan, Russia, Tajikistan, Turkmenistan, Uzbekistan; N Africa, SW Asia, Europe; introduced in the Americas and Australia].