Yellow iris

Yellow iris (Iris pseudacorus), 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 1800s 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 it is known to absorb heavy metals.

Yellow iris can grow in both treed and open 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 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 many American states, and in temperate areas worldwide. Several American states ban it or list it as a noxious weed.

Impacts of yellow iris

• Yellow iris can form dense stands with very thick mats of rhizomes and dead leaves that can displace native plants and change wetlands from a wet to a drier environment.
• The plant reduces habitat available for wildlife, including native fish habitat and bird nesting and rearing sites.
• The dense mats can block water flow in irrigation and flood control ditches.
• 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 centimetres to one metre tall that grow in groups of two to 10.
• Leaves are flattened, two to three centimetres wide and up to one metre long, fanning out from the base.
• Seeds are closely packed in rows of three within capsules four to eight centimetres 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 centimetres long, stems 20 to 60 centimetres 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. Native plants provide habitat and food sources for native wildlife. 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, and seeds may sprout.
• If you find yellow iris or other invasive species in the wild, please contact the toll-free Invading Species Hotline at 1-800-563-7711, or visit Ontario's invading species awareness program and click on Report a Sighting.

Other resources

• Invasive Species Centre
• Stop the spread of invasive species
• Ontario Invasive Plant Council
• Ontario’s Invading Species Awareness Program

For more information

Please contact the Invading Species Hotline at 1-800-563-7711.

© Queen’s Printer for Ontario, 2012

Cette publication est également disponible en français.