Background

Yellow iris, or yellow flag iris, is a perennial aquatic plant native to Europe, Western Asia, and North Africa. It was first introduced to North America in the 19th century as an ornamental plant for ponds and water gardens. The plant has since spread to many waterways, including those in parts of Southern Ontario. In addition to its use in gardens, it has been planted in wastewater ponds because of its ability to absorb heavy metals.

Yellow iris can grow in wetlands, along river and lake edges, and on floodplains. The plant spreads by seeds and by underground stems known as rhizomes that send out new shoots above the ground and roots below. Stands of yellow iris develop thick mats of rhizomes that can connect several hundred plants. Fragments of rhizomes that break off can also form new plants.

Range

The first recorded Canadian sighting of yellow iris was in Newfoundland in 1911. It was later found in Ontario in 1940. Today, it grows in most Canadian provinces, including parts of Southern Ontario, Quebec, Nova Scotia, Newfoundland, New Brunswick, the east coast of Prince Edward Island, and the west coast of British Columbia. It is also found in the United States and in many temperate areas worldwide. Several American states have this plant banned or listed as a noxious weed.

For an up to date distribution map of yellow iris in Ontario, visit www.EDDMapS.org/distribution.

Impacts of Yellow Iris

• Yellow iris can form dense stands with thick mats of rhizomes and dead leaves that can displace native plants and dry out wetlands, altering the ecosystem for its residents.
• The dense mats can also block water flow in irrigation and flood control ditches.
• The plant reduces habitat available for wildlife, including native fish habitat and bird nesting and rearing sites.
• Yellow iris is poisonous to both humans and animals, if eaten, and its sap can cause dermatitis.

How to Identify Yellow Iris

• Flowers have three drooping, deep-yellow sepals with purple-brown markings that look like large petals, surrounding three smaller upright petals.
• Yellow iris is the only iris in North America with entirely yellow flowers.
• Flowers bloom between April and July at the top of stems 30 cm to 1 m (1 – 3 ft) tall that grow in groups of 2 to 10.
• Leaves are flattened, 2 – 3 cm (0.8 – 1.2 in) wide and up to 1 m (3 ft) long, fanning out from the base.
• Seeds are closely packed in rows within capsules 4 – 8 cm (1.6 – 3 in) long.

When not flowering, yellow iris looks similar to the native blue flag iris (Iris versicolor). Blue flag iris is usually smaller, with leaves 10 to 80 cm long, stems 20 to 60 cm long, and purple-to-blue flowers. Yellow iris leaves may also be confused with other wetland plants, such as cattails (Typha spp.) and sweet flags (Acoraceae spp.).

What You Can Do

• Learn how to identify yellow iris and other invasive plants and avoid planting invasive plants in your garden.
• Buy native or non-invasive plants from reputable garden suppliers. See Grow Me Instead: Beautiful Non-Invasive Plants for Your Garden.
• Dispose of invasive plants in the garbage. Do not put them in the compost or discard them in natural areas. Discarded flowers may produce seeds, which may sprout.
• If you find yellow iris or another invasive species in the wild, please contact the toll-free Invading Species Hotline at 1-800-563-7711, visit EDDMapS, or search for the ‘Invasive Species in Ontario’ project on iNaturalist.org to report a sighting.

Resource Files

Other Resources

• Ontario Ministry of Natural Resources and Forestry
• Ontario Invasive Plant Council
• Invasive Species Centre

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