in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 5: 176. 1836.
Perennials, 50–200 cm. Stems (from short caudices) single, branched distally, glabrous throughout, gland-dotted. Leaves opposite (proximal) or alternate (nodes often appearing leafy by development of leaves on lateral buds without axis elongation); petiolate or sessile; blades (usually pinnately or ternately lobed) or lobes 1-nerved or pinnately nerved, linear, 20–100 × 0.2–0.5(–1) mm, bases slightly expanded, margins entire, apices rounded to acute, faces sparsely puberulent to glabrate, gland-dotted. Heads in paniculiform arrays (branches supporting heads recurved, secund). Phyllaries 6–10 in 1–2 series, lanceolate, 1.5–3 × 0.5–0.7 mm, apices acuminate, mucronate, abaxial faces glabrous or glabrate (not gland-dotted). Florets 5; corollas 2–2.5 mm. Cypselae 1–1.5 mm; pappi of 15–30 bristles 2–2.5 mm. 2n = 20.
Phenology: Flowering Aug–Oct.
Habitat: Pond margins, wet, low places, shallow water
Elevation: 10–50+ m
Ala., Fla., Ga., Miss., N.C., S.C.