Iris douglasiana Herbert and I. missouriensis Nutt. are regulated in California (United States); I. pseudacorus is regulated in Vermont (United States).
Perennial. Creeping rhizome. Leaves rigid, flat, smooth and elongate-linear, distichous, equitant, overlapping each other but appearing to be in a rosette. Inflorescence a solitary flower or panicle. Flowers large, showy, subtended by a spathe-like bract; perianth of 6 tepals in 2 similar series; outer series deflexed, inner series erect. Dispersal by rhizome division and seeds.
wet ground and littoral region of lakes, swamps, and rivers