Yellow Flag Iris (Iris pseudacorus)

Yellow flag iris is a popular ornamental in North America that is planted in natural and artificial wet areas within urban and rural landscapes. It is particularly popular as a large and colorful flowering element in ponds and has been planted in wastewater ponds where it is used to remove heavy metals. Unfortunately, I. pseudacorus commonly escapes from cultivation. The species has naturalized extensively and is currently distributed across the United States.

Yellow flag is a very showy species growing 3-4 feet in height with the most vigorous growth attained in the wettest environments. The leaves are long, flattened and sword-like. Large plant clumps are formed from the lateral growth of rhizomes sometimes attaining 20 feet in width. Flowers are produced on erect plant stalks with multiple flowers produced on each. Fruit capsules are large, 3-angled and up to 4 inches in length. Disk-like seeds are shed from the capsules throughout the fall and winter. Floating mats of seed can be observed in backwaters and marshes aiding dispersal.

Impacts

An infestation of yellow flag iris presents a dual impact on both human interests and native environments. Irrigation canals and flood control ditches can be severely restricted by the physical nature of the plant clumps. Removal can be costly requiring large excavation equipment or herbicides. Control of heavily infested waterways can be cost prohibitive due to the huge volume of plant material needing to be removed. Any rhizome fragments that remain quickly reestablish a population. Invaded marshes in some eastern states are experiencing a significant displacement of native sedges and rushes with monocultures of iris. Many over-wintering waterfowl species are dependent on sedge and rush seeds as a high-energy food source. Replacement of this food source with yellow flag iris reduces the carrying capacity of these marshes to sustain waterfowl populations.

AIS Reporting. If you think you’ve found an AIS in Oregon, please report your finding to the

Oregon Invasive Species Online Hotline, 1-866-INVADER

The information used for Aquatic Invasive Species Profiles was created by the Oregon Invasive Species Council as part of the Invasive Species Digital Information Hub

References

Daryl Nolan. 2022. Photo 206467244, no rights reserved, uploaded by Daryl Nolan. iNaturalist. https://www.inaturalist.org/photos/206467244
[FNA] Flora of North America Editorial Committee, eds. 2024. Flora of North America North of Mexico [Online]. 22+ vols. New York and Oxford. Website http:// floranorthamerica.org. [accessed December 2024].
[GISD] Global Invasive Species Database. http://www.iucngisd.org/gisd/ [Accessed February 2024].
[JFP] Jepson Flora Project (eds.). 2024. Jepson eFlora. https://ucjeps.berkeley.edu/eflora/ [Accessed December 2024].
Oregon Department of Agriculture. "B" Rated Weeds Yellow Flag Iris. https://www.oregon.gov/oda/shared/Documents/Publications/Weeds/YellowFlagIrisProfile.pdf
Peter Gabler. 2022. Photo 75753203, no rights reserved, uploaded by Peter Gabler. iNaturalist. https://www.inaturalist.org/photos/75753203
prodewald. 2024. Photo 426037225, no rights reserved, uploaded by prodewald. iNaturalist. https://www.inaturalist.org/photos/426037225
OregonFlora. 2024. OregonFlora database and website. Oregon State University, Corvallis, OR. Website: http://oregonflora.org [accessed December 2024].

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