Ludwigia palustris

Procumbent or ascending glabrous perennial herb; stems branched, floating, to 50 cm long, rooting at nodes. Leaves opposite, broadly elliptic to more or less ovate, 0.5–2.5 cm long, 3–17 mm wide, entire; petiole 2–25 mm long. Flowers sessile, solitary or often paired in upper leaf axils; bracteoles minute, often caducous; sepals 4, green, c. 1 mm long, deltoid, acute; petals absent; stamens 4; ovary 4-celled. Fruit a 4-angled elongate-globose capsule, 2–5 mm long, readily and irregularly dehiscent; seeds free. Flowers mostly Dec.–May.