Helianthus giganteus is a perennial herb, roots fleshy, thickened, stems 1-3 m tall, usually hairy.
Leaves opposite near base, alternate above, stalk short, blade 8-20 cm long, 1-3.5 cm wide, lance-shaped, rough above, usually hairy below, tip long-pointed, 3-veined at base, margin toothed to almost smooth.
Flowers yellow, rays 10-20, 1.5-3 cm long, disk yellow, 1.5-2.5 cm wide, basal bracts of head narrow, thin, loose, hairy, often longer than disk, tips long-pointed; infflorescence of one to a few heads at branch tips; blooms and fruits July-Oct.
Fruit dry, 1-seeded, an achene.
Wetland status: FACW.
Frequency in NYC: Very infrequent.
Habitat: Wet woods, swamps, rich thickets.