Sium serrum (Franchet et Savatier) Kitagawa.

Plants annual, 40–70 cm, slender, glabrous. Roots fusiform, sometimes clustered. Stem erect, much branched above, rooting at the basal nodes. Basal and lower petioles 4–9 cm; blade ternate or 1-pinnate, pinnae 2 pairs; leaflets oblong-ovate or ovate, 5–7 × 2–4 cm, margins serrate, teeth cartilaginous, lateral leaflets sessile, terminal leaflets petiolate. Upper leaves usually reduced, 3-lobed, lobes oblong-ovate or lanceolate, 5–20 × 3–8 mm. Inflorescence much-branched, umbels 2.5–4 cm across; bracts absent, occasionally 1, lanceolate, 2–5 mm; rays 3–4, 1–3 cm, subequal; bracteoles 2–3, lanceolate, 0.5–2 mm, spreading; umbellules ca. 10 mm across, 3–5-flowered; pedicels 2–6 mm, elongating to 15 mm in fruit. Calyx teeth obsolete. Petals white, ovate, apex with an incurved lobule. Stylopodium low-conic; styles 0.75–1 × stylopodium, spreading. Fruit ovoid, ca. 3 × 1.8 mm, base cordate, surface glabrous; vittae 3 in each furrow, 4–6 on commissure. Seed face plane. Fl. and fr. Jul–Sep.

Recent molecular studies uphold Kitagawa’s placement of this species in Sium.

Streamsides; 800–900 m. Anhui [Japan].