Disclaimer:

The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

---

Common name: yellow iris

Synonyms and Other Names: Flag iris, paleyellow iris, pale-yellow iris, yellow flag, yellow flag iris, tall yellow iris, water flag, water iris, European yellow iris, Iris pseudoacorus, Iris pseudocorus, Iris pseudacoris

Taxonomy: available through www.itis.gov

Identification: Iris pseudacorus is a perennial, emergent aquatic plant ranging from 0.5–1.5 m in height (Campbell et al. 2010, Forest Health Staff 2006). Its inflorescence units consist of 4–12 flowers per stem; 6–9 cm spathes are green with brown margins. The outer spathe is strongly keeled, while the inner is without keel; they are subequal and the margins are not dry or membranous. Bright yellow flowers are approximately 7–9 cm wide and occasionally have brown/purple veins at the base of lanceolate to spatulate petals (Lui et al. 2010, Noxious Weed Control Program 2009). Each flower has three downward sepals (5–7.5 cm by 3–4 cm) and three upward petals (2–3 cm) and a floral tube 0.6–0.8 cm (Lui et al. 2010). Flowers typically bloom from April-June (Forest Health Staff 2006). Fruit are prismatic, 6-angled, glossy green capsules (3.5–8.5 cm); individual plants may produce up to 6 pods (Campbell et al. 2010, Jacobs et al 2011). Each capsule may release up to 120 lustrous brown, flattened, D-shaped seeds (6–7 mm), but a small fraction of these are actually viable (Campbell et al. 2010, Jacobs et al. 2011). The corky seeds are buoyant, with 95% of them able to float for up to 2 months (Forest Health Staff 2006, Jacobs et al. 2011, Lui et al. 2010, Noxious Weed Control Program 2009).
The basal deciduous leaves are smooth, stiff, broad, dark green with a gray/blue cast and have a central ridge (40–100 cm by 2–3 cm) (Forest Health Staff 2006, Lui et al. 2010). Stems are usually solid, unbranched, and 70–150 cm in length (Lui et al. 2010). The plant remains green during mild winters (Noxious Weed Control Program 2009).

The fleshy roots are about 10–30 cm long (Lui et al. 2010). This species also has numerous, thick, pink tuberous rhizomes (2–3 cm in diameter) that are freely branching and may form extensive clumps (Noxious Weed Control Program 2009). If broken, rhizomes release black sap (Jacobs et al. 2011).

When not in bloom, it can be difficult to distinguish I. pseudacorus from native irises (Lui et al. 2010, Sarver et al. 2008). It can be distinguished from Northern blue flag iris, which has a three-angled seed capsule (yellow iris has a six-angled capsule) (Campbell et al. 2010). When in bloom, it is easy to distinguish because it is the only iris that grows completely yellow in natural environments (Goodridge et al. 2011).

Size: 0.5-1.5m tall

Native Range: Eurasia.

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Iris pseudacorus is a hearty, perennial monocot found in nutrient rich (especially nitrogen) environments such as wetlands, swamps, floodplain forests, and wet shores of rivers and lakes (Forest Health Staff 2009, Kim et al. 2009, Vymazal and Kröpfelová 2008). Plants are highly tolerant to anoxic conditions and are able to grow vigorously in water/wet soil with a wide range of pH values (Blokhina et al. 2003, Forest Health Staff 2009). Iris pseudacorus also tolerates salt, but grows taller as soil salinity decreases (Sutherland and Walton 1990). While initial colonization may be favored in silty areas, colonies can also root in pebbly/rocky substrate associated with stream riffles (Jacono 2001).

Plants require three years of growth before they reach maturity and are able to flower (Tyron 2006 in Noxious Weed Control Program 2009). Iris pseudacorus is pollinated by long-tongues flies and bumblebees, including Bombus pagans, B. ferpidus, and B. pennsyhankus (Dieringer 1982, Noxious Weed Control Program 2009). Buoyant seeds spread in flowing water and will germinate along shore edges; they typically do not germinate while immersed in water (Noxious Weed Control Program 2009). Iris pseudacorus also forms thick, tuberous rhizomes that spread radially to produce large clonal populations of up to several hundred flowering “individuals”. These populations form dense, underwater mats of vegetation (ISCBC 2012). Rhizomes can split to produce up to 10 plants per year (Je´han et al. 1994 in Kim et al. 2009). These rhizomes are drought tolerant, but during floods, both rhizomes and seeds may be transplanted downstream (Sutherland 1990).

Germination from seed is moderately successful. Sutherland (1990) reported a germination rate of 48% from freshly collected seed in the British Isles, yet in the field found seedlings to be rare in most habitats (Britain and Europe). In western Montana seedlings of Iris pseudacorus are numerous (Preece 1964). Fresh seed collected from plants escaping cultivation in a north Florida swamp exhibited a germination rate of 62% (Jacono and Ramey, unpublished data).

Yellow iris is poisonous; insects and animals tend not to feed on this plant in its native range (Forest Health Staff 2006).

Means of Introduction: Yellow iris is a horticultural favorite and often escapes cultivation to spread locally along shorelines, stream flats, and into fresh and brackish marshes. It is planted for its showy yellow spring flowers having sepals (falls) faintly etched in brown or purple and for its erect, flat, swordlike leaves.

Status: Established.

Impact of Introduction: By 1970 yellow iris was found growing to the complete exclusion of Typha and other native marsh plants along the Merced River in California (Raven and Thomas 1970). It currently occurs along 1300 miles of irrigation canals and laterals near Flathead Lake in northwestern Montana (Lake County Weed District, Pablo, Mont., pers. comm. 2001).

Remarks: The Frio River's water originates from a deep artesian source and remains cool year round. This factor likely contributes to the unusual aggressiveness of this European, normally colder climate species, in the southern U.S.

Many thanks to Clare Lee, US Fish and Wildlife Service, for contributing photographs and occurrence information.

References: (click for full references)

Ahmed, A.H., and E.M. El Hamshary. 2005. Larvicidal, miracidiacidal and cercaricidal acitivites of the Egyptian plant Iris pseudacorus. Journal of the Egyptian Society for Parasitology 35(1):41—48.

Barbolani, E., M. Clauser, F. Pantani, and R. Gellini. 1986. Residual heavy metal (Cu and Cd) removal by Iris pseudacorus. Water, Air, and Soil Pollution 28:277—282.

Benson, A.J., C.C. Jacono, P.L. Fuller, E.R. McKercher, and M.M. Richerson. 2004. Summary Report of Nonindigenous Aquatic Species in U.S. Fish and Wildlife Service Region 5. U.S. Fish and Wildlife Service. Arlington, VA. 145 pp.

Blokhina, O., E. Virolainen, and K.V. Fagerstedt. 2003. Antioxidants, oxidative damage and oxygen deprivation stress: a review. Annals of Botany 91:179—194.

Bossuyt, B., B. De Fré, and M. Hoffman. 2005. Abundance and flowering success patterns in a short-term grazed grassland: early evidence of facilitation. Journal of Ecology 93:1104—1114.

Campbell, S., P. Higman, B. Slaughter, and E. Schools. 2010. A Field Guide to Invasive Plants of Aquatic and Wetland Habitats for Michigan. Michigan DNRE, Michigan State University Extension, Michigan Natural Features Inventory. 90 pp.

Clark, F.H., C. Mattrick and S. Shonbrun (eds.). 1998. Rogues Gallery: New England's Notable Invasives. New England Wild Flower. New England Wildflower Society. Vol. 2, No. 3. pp. 19—26.

Cooper, M.R. and A.W. Johnson. 1984. Poisonous plants in Britain and their effects on animals and man. Her Majesty's Stationery Office, London, England.

Cox, G.W. 1999. Alien species in North America and Hawaii: Impacts on Natural Ecosystems. Island Press, Washington, DC. 400 pp.

Dieringer, G. 1982. The pollination ecology of Orchis spectabilis L. (Orchidaceae). Ohio Journal of Science 82(5):218—225.

Falck, M. and S. Garske. 2003. Invasive Non-native Plant Management During 2002. Administrative Report 02-12. Great Lakes Indian Fish & Wildlife Commission (GLIFWC). Odanah, WI. 68 pp.

Falck, M., S. Garske, and D. Olson. 2010. Invasive Species Program 2009. Administrative Report 10-11. Great Lakes Indian Fish & Wildlife Commision. Odanah, WI. 36 pp.

Falck, M., L. Hill, and R. Parisien. 2011. Invasive Species Program 2010. Administrative Report 11-11. Great Lakes Indian Fish & Wildlife Commission. Odanah, WI. 27 pp.

Falck, M., W. Gilane, and R. Parisien. 2012. Invasive Species Program 2011. Administrative Report 12-02. Great Lakes Indian Fish & Wildlife Commission. Odanah, WI. 27 pp.

Forest Health Staff. 2006. Yellow Iris: Iris pseudacorus L. Weed of the Week. U.S. Department of Agriculture Forest Service. Newton Square, PA. Available http://na.fs.fed.us/fhp/invasive_plants/weeds/yellow-iris.pdf

Great Lakes Panel on Aquatic Nuisance Species (GLPANS). 2008. Prohibited Species in the Great Lakes Region. Great Lakes Commission, Ann Arbor, MI. 14 pp.

Goodridge, J., M. Bixby, L. Winter-Gorsline, M. Tu, S. Anderson, R. Harber, J. Douglas, L. McMahan, and S. Chan. 2011. GardenSmart Oregon: a guide to non-invasive plants. The Nature Conservancy, Oregon Invasive Species Council. Portland Oregon. 54 pp.

The Idaho Invasive Species Council Technical Committee. 2007. Idaho Aquatic Nuisance Species Plant. A Supplement to Idaho's Strategic Plant for Invasive Species. 139 pp.

Invasive Species Council of British Columbia (ISCBC). 2012. Yellow Flag Iris. BC's most 'unwanted' Invasive Plants. Available http://www.bcinvasives.ca/invasive-species/invasive-plants/yellow-flag-iris. Accessed 9 July 2012.

Jacobs, J., M. Pokorny, J. Mangold, and M. Graves-Medley. 2011. Biology, Ecology and Management of Yellowflag Iris (Iris pseudacorus L.). Montana State University Extension. Bozeman, MT. 12 pp.

Jacono, C.C. 2001. Iris pseudacorus. USGS Nonindigenous Aquatic Species Program. Available http://nas.er.usgs.gov/taxgroup/plants/docs/ir_pseud.html Accessed 23 August 2012.

Jéhan, H., D. Courtois, C. Ehret, K. Lerch, and V. Pétiard. 1994. Plant regeneration of Iris pallida Lam. and Iris germanica L. via somatic embryogenesis from leaves, apices and young flowers. Plant Cell Rep 13:671—675.

Kim, T.D., C.H. Ahn, K.H. Bae, and Y.E. Choi. 2009. The embryogenic competency and morphological changes during somatic embryogenesis in Iris pseudacorus. Plant Biotechnology Report 3:251—257.

Larue, C., N. Korboulewsky, R. Wang, and J.P. Mévy. 2010. Depollution potential of three macrophytes: Exudated, wall-bound and intracellular peroxidase activities plus intracellular phenol concentrations. Bioresource Technology.

Latimore, J.A., P. Filice, E. LaPorte, and S. Ariganello. 2011. Clean Boats, Clean Waters. Guidelines for Clean Boats, Clean Waters: Michigan's Aquatic Invasive Species Volunteer Program Handbook. Michigan Sea Grant and the Great Lakes Restoration Initiative. 35 pp.

Lui, K., M. Butler, M. Allen, E. Snyder, J. da Silva, B. Brownson, and A. Ecclestone. 2010. Field Guide to Aquatic Invasive Species: Identification, collection and reporting of aquatic invasive in Ontario waters. 3rd Edition Ministry of Natural Resources. Ontario, Canada. 201 pp.

Minnesota Department of Natural Resources (MNDNR). 2012. Yellow iris (Iris pseudacorus). Invasive terrestrial plants. Available www.dnr.state.mn.us/invasives/terrestrialplants/herbaceous/yellowiris.html. Accessed 11 June 2012.

Minnesota Invasive Species Advisory Council. 2009. A Minnesota state management plan for invasive species. 76 pp.

Monk, L.S., K.V. Fagerstedt, and R.M.M. Crawford. 1987. Superoxide dismutase an in anaerobic polypeptide: a key factor in recovery from oxygen deprivation in Iris pseudacorus? Plant Physiology 85(4):1016—1020.

The Nature Conservancy. n.d. Yellow-Flag Iris. Invasive fact sheet. Montpelier, VT. 2 pp. Available http://www.nature.org/ourinitiatives/regions/northamerica/unitedstates/vermont/yellowiris2010-2.pdf

New York Invasive Species Council. 2010. Final report: a regulatory system for non-native species. Department of Environmental Conservation. Albany, NY. 131 pp.

Noxious Weed Control Program. 2009. Yellow-flag iris (Iris pseudacorus). Best Management Practices. Department of Natural Resources and Parks; Water and Land Resources Division. King County, WA. 7 pp.

Ohio Department of Natural Resources (OHDNR). 2012. Rare native Ohio plants 2010-2011 Status List. Available http://dnr.state.oh.us/Home/Rare_Plants/20102011RareNativeOhioPlants/tabid/22557/Default.aspx. Accessed 17 May 2012.

Ohio Division of Natural Areas and Preserves, and The Nature Conservancy. 2000. Ohio's Invasive Plant Species. 2 pp.
Oregon Department of Agriculture (ODA) Plant Division. 2012. Yellow flag iris (Iris pseudacorus). Noxious Weed Control Available http://www.oregon.gov/ODA/PLANT/WEEDS/profile_yflagiris.shtml. Accessed 13 June 2012.

Preece, S.J. 1964. Iris pseudacorus in Montana. Proceedings of the Montana Academy of Sciences 24:1—4.

Piccardi, E.B., and M. Clauser. 1983. Absorption of copper by Iris pseudacorus. Water, Air, and Soil Pollution 19:185—192.

Raven, P.H. and J.H. Thomas. 1970. Iris pseudacorus in western North America. Madrono 20:390—391.

Rubtzoff, P. 1959. Iris pseudacorus and Caltha palustris in California. Leaflets of Western Botany 9(2):31—32.

Sanavova, M.Kh., and D.A. Rakhimov. 2004. Iris polysaccharides. III. Carbohydrates from Iris pseudacorus. Chemistry of Natural Compounds 40(1):83—84.

Sarver, M., A. Treher, L. Wilson, R. Naczi, and F.B. Kuehn. 2008. Mistaken Identity? Invasive Plants and their Native Look-Alikes: an Identification Guide for the Mid-Atlantic, Delaware Department Agriculture. 68 pp.

Schlüter, U., and R.M. Crawford. 2001. Long-term anoxia tolerance in leaves of Acorus calamus L. and Iris pseudacorus L. Journal of Experimental Botany 52(364):2213—2225.

Sturtevant, E.L., and U.P. Hedrick (eds.). 1972. Sturtevant’s Edible Plants of the World. Dover Publications. 775 pp.

Sutherland, W.J. 1990. Iris pseudacorus L. Journal of Ecology 78(3):833—848.

Sutherland, W.J., and D. Walton. 1990. The changes in morphology and demography if Iris pseudacorus L. at different heights on a saltmarsh. Functional Ecology 4(5):655—659.

Tyron, P. 2006. Yellow Flag Iris Control, in the Mission Valley of Western Montana. Presented at the 2006 Washington State Weed Conference.

Tu, M. 2003. Element Stewardship Abstract for Iris pseudacorus L. (yellow flag iris, water flag). The Nature Conservancy. Arlington, Virginia. 11 pp. Available http://www.invasive.org/weedcd/pdfs/tncweeds/irispse.pdf

United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS). 2012. Plants Database. Available http://plants.usda.gov/java/. Accessed 27 June 2012.

U.S. Environmental Protection Agency (USEPA). 2008. Predicting future introductions of nonindigenous species to the Great Lakes. Washington DC. 138 pp.

Vymazal, J., and L. Kröpfelová. 2008. Wastewater treatment in constructed wetlands with horizontal sub-surface flow: environmental pollution. Volume 14. Springer Science. Ch. 5 & 6.

Wu, H., J. Zhang, P. Li, J. Zhang, H. Xie, and B. Zhang. 2011. Nutrient removal in constructed microcosm wetlands for treating polluted river water in northern China. Ecological Engineering 37:560—568.

Yakima, W.A. 2009. Lake County Weed Control in Noxious Weed Control Program. Ignatius, MT.

Zhang, X.B., P. Liu, Y.S. Yang, and W.R. Chen. 2007. Phytoremediation of urban wasterwater by model wetlands with ornamental hydrophytes. Journal of Environmental Sciences (China) 19(8):902—909.

Other Resources:
Invasive Plant Atlas of New England

 

US Fish and Wildlife Service Ecological Risk Screening Summary for Iris pseudacorus

Author: Morgan, V.H., L. Berent, and A. Fusaro

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.