The Yellow Flag Iris is a native of Europe, northwestern Asia and northern Africa. A wetland Iris, pseudacorus propagates aggressively by both rhizomes and prolific self seeding.

Per the USDA Plants Database, Noxious Weed Information:
Connecticut: Invasive, banned
Massachusetts: Prohibited
Montana: Category 3 noxious weed
New Hampshire: Prohibited invasive Species
Oregon: "B" designated weed, Quarantine
Washington: Class C noxious weed

Additional invasive resources listing I. pseudacorus include “The Invasive Plant Atlas of the United States” http://www.invasiveplantatlas.... and “Invasive Plants of the U.S.” http://www.invasive.org/weedcd...

Numerous sterile cultivars and hybrids of I. pseudacorus, notably the Pseudatas (I. pseudacorus x I. ensata), are available today for growing outside its native range.

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This is a Class C noxious invasive in the Pacific Northwest. Control is recommended but not required. It may sicken livestock although it is generally avoided by herbivores. It clogs small streams and irrigation systems, displaces native vegetation along streambanks, and reduces habitat for waterfowl and fish. It spreads quickly into large clumps in shallow water. It can be pulled by hand or machine, although some folks react to the resins in the leaves and rhizomes. It is extremely difficult to get all the roots and I have had poor luck trying to clear this thug from my pond (we've dug them up using a backhoe). I have also read that one can persistently cut all leaves and stems below the waterline, but have not tried that method. On the plus side, it is a pretty plant with showy yellow flowers. It is native to Europe, the Mediterranean, North Africa, and Asia Minor.

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