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Yellowflag iris

(Iris pseudacorus)

Erect perennial up to 1.2 meters (4 feet) tall and found in wet areas.  Native of Europe and Africa. Introduced as an ornamental in the early 1900’s.

Quick Identification:

• Showy yellow flowers.
• Long, sword-like leaves.
• Only completely yellow-flowered iris in North America.
• Forms dense colonies in wet areas.

Interesting Facts:

Has been used for erosion control, sewage treatment, and is known to remove metals from wastewater. Can be toxic to humans and animals. Yellow flag iris continues to be sold through garden dealers.


Digging can successfully control small, isolated patches if the entire rhizome mass is removed and treatment is repeated every year for several years to weaken and eventually kill the plant. Wear gloves.

Reproduction and Dispersal:

By rhizomes and seeds. Seeds germinate and grow well after being burnt. Mainly spread by people but can fragment and spread down water ways.

Habitat Preference:

Found in moist soils near lakes and ponds, stream banks, irrigation ditches and wetlands.


This plant increases steam sedimentation which affects fish.  It can grow big enough to block stream access and can alter flows causing stream bank erosion.  Once established it is a hard work to remove.


One to several large, yellow flowers on each stem; has three upward pointing petals and three downward pointing, tongue shaped sepals; often adorned with brown spots or purple veins.

Leaves and Stems:

Leaves are 0.5 to 1 meter long, sword-like, flat, with pointy tip; 8 to 25 mm wide; raised midribs and smooth edges; arranged with sheathing, fan-like. Branched, flowering stems have few to no leaves.


Fruit is an erect, three-chambered, glossy-green cylindrical capsule. Each chamber contains many disc-shaped, pitted, pale brown seeds densely packed in vertical rows.


Thick, fleshy rhizomes may extend 10 to 20 cm (4-8 inches) deep. Rhizomes often form horizontal mats, and can grow for several months without water.

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