Yellow iris (Iris Pseudacorus) is a flowering plant native to North Africa, Europe, and Asia, that is identifiable by its bright yellow flower, which led to its popularity as an ornamental plant. Since its introduction in the late 1700s, the popularity of the yellow iris throughout history has contributed to its continued spread.

Habitat: Yellow-flag iris grows along the edges of rivers, ponds, streams, open and forested flood plains, and along freshwater shorelines. wetlands and marshes.  


Yellow-flag iris forms dense monotypic stands and expands quickly via rhizomes. It can easily replace and crowd out important riparian plants causing a loss of vital habitat. Additionally, the root systems of yellow-flag iris can narrow waterways and clog irrigation systems. All parts of the plant are toxic to livestock and other animals. 

European water chestnuis an aquatic plant, which is usually rooted in the mud; it bears a rosette of floating leaves at the tip of the submersed stem. Although it grows best in shallow, nutrient-rich lakes and rivers, it can also grow on wet, mucky substrates. Stems – Stems are elongate, flexuous and typically about a meter long but may reach as much as 5 meters in length.
Leaves – The conspicuously toothed leaf blades are ½-1 inch long and rhombic in outline (with four sides); the spongy, inflated leaf stalks are up to 3 inches long and provide the buoyancy to keep the terminal leafy portion of the plant floating at the water surface. Green, feather-like, submersed leaves (considered by some to be modified roots) with very fine segments are present on the underwater portion of the stem.
Roots – Numerous finely branched roots develop along the lower stem and assist in anchoring the plant to the substrate.
Flowers – The inconspicuous flowers with their four white petals, each about 1/3 inch long, are borne singly on erect stalks located in the central area of the leafy rosette.
Fruit – The fruit is a black, four-horned, nut-like structure, about an inch wide, that develops under water


When it’s not flowering, yellow-flag iris can be easily confused with native blue-flag iris and other wetland plants such as cattails or sweet flag. Use the characteristics described below to help identify yellow-flag iris. 

Leaves are a dark blueish-green color, long and flat with a distinctive midrib that runs the length of the leaf. Leaves stand upright between 1 -7 feet tall and have a sword-like appearance. Stems grow among the leaves at the same height or taller and from multiple flower buds at the top. 

Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Flowers are pale to bright yellow and appear in spring to early summer. Flowers are 3-4 inches wide and have three upright petals and three larger downward-pointing sepals which may have brown to purple-colored markings. 

Shaun Winterton, Aquarium and Pond Plants of the World, Edition 3, USDA APHIS PPQ, Bugwood.org

Roots form at the base of leaves above and along the rhizomes and are 10-30 CM in length and white. Rhizomes are thick and fleshy 1-4 inches in diameter with a pinkish-orange color to them. The color of the roots can help distinguish the invasive yellow-flag iris from the native blue-flag iris which has white-colored rhizomes.  

Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Fruits are 4-8 CM long capsules with angled edges. Seeds are in densely packed rows inside the capsule that harden and turn brown as they mature. 

Leslie J. Mehrhoff, University of Connecticut, Bugwood.org


Physical/Mechanical Control: Depending on the size of the infestation, yellow-flag iris can be managed by using shovels to dig up the rhizomes. Take care to remove all of the rhizomes to reduce resprouting. Gloves should be worn as the sap of yellow-flag iris can cause skin irritation. 

Multiple mowings can help to weaken the plant but regrowth will occur if the rhizomes are not removed. 

Chemical Control: Larger infestations of yellow-flag iris can be controlled by herbicides approved for aquatic use. Herbicides can be more effective when applied to recently cut foliage and stems. 

Always check state and local regulations for permitting requirements and follow all chemical label instructions. 


Prevent the introduction of invasive species into the SLELO PRISM.

Rapidly detect new and recent invaders and eliminate all individuals within a specific area.

Share resources, including funding personnel, equipment, information, and expertise.

Collect, utilize, and share information regarding surveys, infestations, control methods, monitoring, and research.

Control invasive species infestations by using best management practices, methods and techniques to include: ERADICATION (which is to eliminate all individuals and the seed bank from an area), CONTAINMENT (which is reducing the spread of established infestations from entering an uninfested area) and SUPPRESSION which is to reduce the density but not necessarily the total infested area.

Develop and implement effective restoration methods for areas that have been degraded by invasive species and where suppression or control has taken place.

Increase public awareness and understanding of invasive species.

Develop and implement innovative technologies that help us to better understand, visualize, alleviate or manage invasive species and their impacts or that serve to strengthen ecosystem function and/or processes.

Rob Williams
PRISM Coordinator

Megan Pistolese
Outreach and Education

Brittney Rogers
Aquatic Invasive Species

Robert Smith
Terrestrial Invasive Species