Yellow Iris

Description

Yellow iris (Iris pseudacorus) is an invasive aquatic plant native to Eurasia and North Africa that was introduced to North America as an ornamental plant. Known for its showy yellow flowers, it grows along shorelines and in wetlands, ponds, streams, and other wet habitats. Yellow iris spreads through both seeds and underground stems called rhizomes, allowing it to form dense patches that crowd out native vegetation, reduce biodiversity, and alter wetland habitats. Despite its invasive impacts, yellow iris is still widely available through the horticultural industry.

  • Scientific name: Iris pseudacorus

  • French name: Iris faux-acore

  • Common name(s): Yellow flag iris, pale yellow iris, yellow water iris or yellow flag. 

  • Regulatory Status: Yellow iris is not a federally regulated invasive plant in Canada. However, it is regulated as Noxious Weed Alberta and British Columbia.  

Image of Yellow Iris

© fboue19 via iNaturalist.org, used under CC-BY-NC

Introduction and Spread

Yellow iris was brought to North America as an ornamental plant and is still widely available in the horticulture industry. It was first recorded in North America in Newfoundland in 1991 (Tu 2003; Denslow et al. 2010; Jacobs 2010). Yellow iris can spread via rhizomes and seeds that can float for extended periods of time, facilitating their spread via water (Sutherland 1990; DiTomaso and Kyser 2016). Several hundred plants can be connected via rhizomes (Morgan et al. 2025) and fragments as small as 2 cm can generate new plants (Jaca 2013). However, most infestations originate from the intentional planting of yellow iris in garden which then spread to nearby natural areas such as wetlands, river, streams and shorelines. It may also be unintentionally transported on contaminated equipment such as seeds or rhizome fragments on boots or spades/shovels used for manual removal. 

Yellow iris is native to Eurasia and North Africa (Tu 2003). In North America, it is found in all states, with the exception of North Dakota and Arizona (EDDMapS 2025). Yellow iris is widespread across Canada and occurs in every province except for Saskatchewan, Manitoba, Yukon, Nunavut and the Northwest Territories. It is listed as noxious weed in British Columbia and Alberta.  

Habitat

Yellow iris grows in or near water, although, it can survive in wet terrestrial environments. This includes in and around streams, rivers, ponds, wet meadows and wetlands. It is also found in disturbed environments such as roadside ditches and stormwater management ponds. It prefers full sun and soils that have high moisture content. It can tolerate salinity, low-fertility soils including those with poor oxygen availability (Tu 2003; Jacobs et al. 2010). 

Identification

  • Height and stem: It has solid stems and can grow between 0.4 m – 1.5 m tall. 

  • Leaves: Blue-green to dark green in colour, broad, flattened, stiff and sword-shaped. They form basal clusters that fan out at the base and can be 50 cm – 100 cm long. 

  • Flowers: Occur on a stalk in groups of 2 – 3. They are pale yellow to orange and composed of six segments. They have three drooping, tongue-shaped sepals with purple veins and spots at the base. It also has three erect, smaller petals. The flowers range between 8 cm – 10 cm wide. 

  • Fruits: Each flower produces an oblong capsule that is 6-sided, glossy-green and leathery that measures 4 cm – 8 cm long. This capsule contains 100 – 120 seeds that have a hard seed coat and internal gas space that allows them to float. 

  • Roots: Yellow iris has an extensive underground roots system, composed of thick, branching, pink-coloured rhizomes. They exude a black sap that is toxic if ingested and can cause skin irritation. 

Image of yellow iris flower

Yellow iris flower

Image of yellow iris fruit

Yellow iris fruit

Image of yellow iris leaves

Yellow iris leaves

Impacts

  • Yellow iris forms thick mats that can float on the surface of water or dense patches of emergent vegetation that lower biodiversity, displaces native plants needed for wildlife such as waterfowl, alter hydrology and sedimentation which can covert wetlands to drier habitats such as wet meadows and forests (Sutherland 1990; Jacobs et al. 2010; DiTomaso and Kyser 2016; Gallego-Tevar et al. 2022).  

  • While yellow iris is still widely available in North America, despite being classified as a noxious weed in many parts of its introduced range, it can be extremely costly to remove once established.  

  • The rhizomes of yellow iris are toxic to animals or humans if ingested. They contain iridin which can cause severe gastrointestinal symptoms. In addition, it can cause skin irritation (Jacobs et al. 2010; DiTomaso and Kyser 2016).  

Life cycle

The leaves of yellow iris emerge in early spring and actively grow from April to June. This typically occurs via its rhizomes that remain dormant over the winter, rather than from new seeds. It reaches sexual maturity at three years old. Flowering occurs between May and June and flowers are pollinated by bumbles and long-tongued flies (Tu 2003; Morgan et al. 2025). Fruits that contain between 32 – 120 seeds ripen and disperse in late summer to early fall. Only a small portion of seeds (up to 20%) are viable (Sutherland 1990; Tu 2003; Gaskin et al. 2016). In the fall, above ground vegetation dies and the plant overwinters via its rhizomes. 

What You Can Do

You can help prevent the spread of yellow iris by:

  • Clean Drain Dry: Inspect your boat, trailer, paddles, fishing gear, and boots for mud, plant parts, or small critters. Remove and dispose of anything you find before leaving the water.

  • Don’t Let it Loose: Never release aquarium or domestic pond water, plants, dead or living animals into waterbodies. 

  • PlantWise: Don't plant yellow iris or other invasive species. Choose native or non-invasive alternatives.  

  • Educate: Learn how to identify yellow iris and spread awareness about the ecological risks posed by invasive aquatic plants and encourage responsible practices in your community.  

  • Reporting: Report yellow iris and any invasive species to the appropriate provincial authorities such as provincial invasive species councils or report using free tools such as EDDMapS and iNaturalist.  

Other Resources

  1. Denslow, M.W., Katz, G. and Jennings, W.F. 2011. First records of Iris pseudacorus (Iridaceae) from Colorado. Journal of the Botanical Research Institute of Texas. 5(1): 327-329. https://www.jstor.org/stable/41972524.  
  2. DiTomaso, J. and Kyser, G. 2016. Shoreline drizzle applications for the control of incipient patches of yellow iris (Iris pseudacorus). Invasive Plant Science and Management. 9: 205-213. https://doi.org/10.1614/IPSM-D-16-00023.1.  
  3. EDDMapS. 2025. Pale yellow iris, yellow flag iris (Iris pseudacorus L.). [Accessed 2025 March 25] https://www.eddmaps.org/distribution/usstate.cfm?sub=5853/.  
  4. Gallego-Tevar, B., Grewall, B.J., Whitcraft, C.R., Futrell, J.C., Barcenas-Moreno, G. and Castillo, J.M. 2022. Contrasted impacts of yellow iris (Iris pseudacorus) on plant diversity in tidal wetlands within its native and invaded distribution ranges. Diversity. 14: 326. http://dx.doi.org/10.1016/S2095-3119(17)61831-8.  
  5. Gaskin, J.F., Pokorny, M.L., and Mangold, J.M. 2016. An unusual case of seed dispersal in an invasive aquatic; yellow iris (Iris pseudacorus). Biological Invasions. 18: 2067-2075. https://link.springer.com/article/10.1007/s10530-016-1151-0  
  6. Jaca, T. 2013. Iris pseudacorus L.: An ornamental aquatic with invasive potential in South Africa. South Africa Journal of Botany. 86: 174. http://dx.doi.org/10.1016/j.sajb.2013.02.133.  
  7. Jacobs, J, Graves, M and Mangold, J. 2010. Ecology and management of yellow flag (Iris pseudacorus L.). United States Department of Agriculture, Natural Resources Conservation Services. Invasive Species Technical Note No. MT-28. https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=106369cd1aa0425afb6afef877876dfa1ed183c2  
  8. Morgan, V.H., Berent, L., and Fusaro, A. 2025. Iris pseudacorus L.: U.S. Geological Survey, Nonindigenous Aquatic Species Database. [Accessed 2025 March 24]. https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?Species_ID=1115   
  9. Sutherland, W.J. 1990. Iris pseudacorus L. Journal of Ecology. 78(3): 833-848. https://doi.org/10.2307/2260902.  
  10. Tarasoff, C., Streichert, K., Gardner, W., Heise, B., Church, J. and Pypker, T. 2016. Assessing benthic barriers versus aggressive cutting as effective yellow iris (Iris pseudacorus L.) control mechanisms. Invasive Plant Science and Management. 9(3): 229-234 
  11. Tu, M. 2003. Element Stewardship Abstract for Iris pseudacorus L. The Nature Conservancy; [Accessed 2025 March 24]. https://www.invasive.org/gist/esadocs/documnts/irispse.pdf. 

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