Perennials; (submerged aquatic, rooting from proximal nodes, forming clumps); glabrous or pubescent proximally on young leaves. Stems prostrate basally (hollow), branched, (2–) 4–12 (–13) dm. Basal leaves not rosulate; blade margins pinnatifid. Cauline leaves (proximal) petiolate, (distal) sessile; blade pectinate or pinnatisect to pinnatifid (especially when submerged), oblanceolate to elliptic, 4–12 cm × 5–30 mm, base auriculate or not, margins entire or denticulate to serrate (emergent ones usually undivided, rarely lobed). Racemes considerably elongated. Fruiting pedicels horizontal to reflexed, straight or recurved, (5–) 7–15 (–18) mm. Flowers: sepals erect, oblong, 2.5–3.5 × 1–1.7 mm; petals yellow, obovate, (3.3–) 3.8–5.5 (–6.2) × 1.5–2.5 mm; median filaments 3–4 mm; anthers ovate, 0.7–1 mm. Fruits silicles, straight, ovoid-oblong, (2.5–) 3–5.5 (–7) × 1.7–2.7 (–3) mm; valves glabrous; ovules 36–62 per ovary; style (0.5–) 1–2.2 (–2.5) mm. Seeds biseriate, reddish-brown, ovoid, 0.7–1 mm (0.5–0.6 mm diam.), colliculate. 2n = 16, 32.

Phenology: Flowering Jun–Aug.
Habitat: Lakeshores, marshes, ponds, streams

Distribution

• Generated Map
• Legacy Map

Introduced; Que., Maine, N.Y., Europe, Asia

Discussion

Selected References

None.

Lower Taxa

None.

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