Eutrochium fistulosum is a perennial herb, much like E. purpureum but larger, to 3 m, stem purple, (usually not spotted), with a conspicuous waxy bloom (strongly glaucous), hollow between nodes.
Leaves in whorls of 4-7, narrowly elliptic to lance-shaped, marginal teeth finer, blunter than those of E. purpureum, pointed at both ends, surface often puckered by impressed veins, veins pinnate.
Flowers purple-pink, about 0.4 cm long, 5-8 per head, no rays; inflorescence dome-topped or pyramidal, 10-50 cm tall 10-30 cm wide, branches divergent; blooms July-Sept.
Fruit dry, 1-seeded, 5-angled plumed achene about 0.4 cm long; winter flower stalks tipped by tiny white button-like receptacles.
Wetland status: FACW.
Frequency in NYC: Infrequent.
Habitat: Marsh edges, wet roadside ditches.