This Class C noxious weed is widespread throughout western Washington. Control is recommended but not required in King County.

Description
When flowering, yellow flag iris is unmistakable with its showy yellow flowers colorfully displayed along the edge of water and in wetlands. In Washington, the flowers occur in late spring or early summer.

Several flowers can occur on each stem, along with one or two leafy bracts. Each flower resembles a common garden iris. The leaves are mostly basal and are folded and clasp the stem at the base in a fan-like fashion. Yellow flag iris is perennial, and will remain green during winter where the weather is mild. It has stout rhizomes and long, spreading roots. Seeds form in large, glossy green, triangular capsules. The seeds are corky. The plants spread rhizomatously and grow tightly bunched together.

This is the only yellow iris found in Washington’s wet areas, but when not flowering it may be confused with cattail (Typha latifolia) or broad-fruited bur-reed (Sparganium eurycarpum). Look for the fruits in the summer, or the fan-shaped plant-base at other times of year.

Yellow flag iris will sicken livestock if ingested, and is generally avoided by herbivores (although muskrats will eat the rhizomes). Contact with the resins can cause skin irritation in humans.

Geographic Distribution
Yellow flag is native to Europe, Great Britain, North Africa and the Mediterranean region. It has been introduced in temperate areas nearly world-wide and occurs throughout the United States.

For more information about yellow flag iris, please see the King County Best Management Practices for Yellow Flag Iris and the written findings of the WA State Noxious Weed Control Board.

More yellow flag iris photos - click on thumbnail for larger image