Aquatic and Wetland Vascular Plants of the Northern Great Plains
34. Apiaceae, the Parsley Family
3. Sium L. -- Water parsnip1. Sium suave Walt.
Stout, fibrous-rooted perennial 4-20 dm tall, from a short erect crown; stems solitary, strongly ribbed upward, thickened and hollow with cross-partitions at the base, partitioned at the nodes above. Leaves once-pinnate, the blades oblong to ovate in outline, 5-25(35) cm long, 6-20(30) cm wide; leaflets usually 7-17 per leaf, linear to lanceolate, 3-15 cm long, 3-15 mm wide, sharply serrate; petioles long below, shorter upward, hollow, septate-nodulose; submersed leaves often present early in the season, finely bipinnately dissected. Umbels terminal and lateral, few to many, 4-12 cm wide in fruit, on peduncles 3-10 cm long; rays 1.5-4 cm long; bracts 6-10, narrowly lanceolate, entire or incised, reflexed; umbellets 7-12 mm wide, the pedicels 3-5 mm long; bractlets 4-8, smaller than the bracts, entire. Flowers white or greenish-white, 1.5-2 mm across; sepals minute or none. Fruits oval to orbicular, 2-3 mm long, slightly constricted on the commissure, the ribs prominent and corky, subequal. Jul--Sep. Marshes, swamps, springs, ditches and margins of streams, ponds and lakes, often emergent; common; (Newf. to B.C., s to FL, TX and CA).
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