Iris pseudacorus is a perennial monocotyledon 50 cm to 1 m, aggressively colonial from pink-fleshed rhizomes 2-3 cm wide, flowering stem shorter than or equal to leaves.
Leaves basal, linear, stiff, erect in fan-shaped arrangement, 0.4–1.0 cm long, 2–3 cm wide, midrib region thickened, apparently wider than those of I. versicolor and more persistent in autumn, veins parallel; old leaves remain as basal fibers (Haller 2007).
Flowers bright yellow, radially symmetrical 7-9 cm wide, 3 short, erect petals 1-2.5 cm long, 3 larger, pendant sepals; inflorescence stem shorter than leaves; blooms April-June.
Fruit dry, 6 angled capsule 5-8.5 cm long, cylindrical, valves opening widely to release seeds.
Wetland status: OBL.
Frequency in NYC: Infrequent.
Habitat: Open marshes, pond margins. Sometimes planted at wetland mitigation sites or landscaping in wet soil (Graniteville swamp forest).
Notes: Iris pseudacorus is quite invasive and listed as a “noxious plant” in several states including CT, MA and NH in the northeastern USA (USDA, NRCS 2006).