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. Flowering Aug-Oct. Pond margins, wet, low places, shallow water; 10-50+ m; Ala., Fla., Ga., Miss., N.C., S.C.