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Brazilian Elodea
Egeria densa

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Eurasian Water-Milfoil
Myriophyllum spicatum

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Hydrocharis morsus-ranae

European Water Chestnut (Trapa natans) photo by OFAH
European Water Chestnut
Trapa natans

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Fanwort
Cabomba caroliniana

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Hydrilla
Hydrilla verticillata

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Parrot Feather
Myriophyllum aquaticum

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Eichhornia crassipes

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Water Lettuce
Pistia Stratiotes

Water Soldier (Stratiotes aloides) photo by Francine MacDonald, MNR
Water Soldier
Stratiotes aloides

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Yellow Floating Heart
Nymphoides peltata

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Yellow Iris
Iris pseudacorus

Yellow Iris
Iris pseudacorus

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 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 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. See Grow Me Instead: Beautiful Non-Invasive Plants for Your Garden. Go to ontario.ca/invasivespecies, click on Here’s a list of things you can do to help fight invasive species, and click on the title
  • 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 report a sighting online.

Other Resources

OFAH/OMNR Invading Species Awareness Program. (2012). Yellow Iris. Retrieved from: http://www.invadingspecies.com. This factsheet may be reproduced for non-commercial purposes.

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Downloads

Icon of Field Guide to Aquatic Invasive Species (3rd Edition) Field Guide to Aquatic Invasive Species (3rd Edition) (3.5 MiB)
Icon of Brochure - Garden Smart Brochure - Garden Smart (2.3 MiB)
Icon of Brochure - Water Gardens Brochure - Water Gardens (1.5 MiB)
Icon of Brochure - Grow Me Instead (Northern Ontario) Brochure - Grow Me Instead (Northern Ontario) (11.9 MiB)
Icon of Brochure - Grow Me Instead (Southern Ontario) Brochure - Grow Me Instead (Southern Ontario) (6.3 MiB)
Icon of Fact Sheet - Yellow Iris Fact Sheet - Yellow Iris (1.0 MiB)