Iris pseudacorus L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Lvs stiff and erect, broadly ensiform from densely crowded rhizomes; stem 0.5–1 m, shorter than or equaling the lvs; fls 7–9 cm wide, bright yellow or cream-color; sep spreading, the crest area outlined by an irregular series of brown markings; pet erect, ligulate, constricted at the middle, 1–2.5 cm, unmarked; capsule 6-angled, cylindric-prismatic to ellipsoid, 5–8.5 cm, the valves widely spreading at maturity; 2n=24–34. Swamps and shallow water along streams and ponds; native of Europe, and widely established in our range. Apr.–June.
water-flag, yellow flag