Reynoutria japonica var. japonica
Japanese Knotweed is often mistaken for bamboo; however it is easily distinguished by its broad leaves and its ability to survive Ontario winters. Japanese Knotweed is especially persistent due to its vigorous root system, which can spread nearly 10 metres from the parent stem and grow through concrete and asphalt. This invader is very persistent and once it becomes established, is incredibly difficult to control.
In Canada, Japanese Knotweed is established from Ontario to Newfoundland and is also found in British Columbia. In Ontario, it is mostly established in southern and central areas of the province where it mostly grows in gardens, along roadsides and near old buildings or former building sites.
Impacts of Japanese Knotweed
- Spreads quickly, creating dense thickets that degrade wildlife habitats.
- Reduces plant biodiversity by competing with other native vegetation. Thick layers of decomposing stems and leaves on the ground make it difficult for native plant species to establish.
- Aggressive plant with a strong root system that has been known to break through asphalt and concrete.
- Plant populations are extremely persistent. Plants are able to survive severe floods and recolonize areas.
- It can establish along riverbanks, where pieces of roots can break off and float downstream to start new populations.
How to Identify Japanese Knotweed
- Semi-woody perennial plant capable of reaching 1-3 metres in height.
- Stems are round, reddish-purple, smooth and have a bamboo-like appearance.
- Leaves are ovate with a flat base, reaching 3-6 inches long and 2-5 inches wide with pointed tips.
- Flowers are greenish-white.
- Fruit is small and white with wings that help to disperse seeds to new sites.
- Seeds are brown and shiny.
What You Can Do
- Learn how to properly identify Japanese Knotweed and how to effectively manage invasive plants on your property.
- Avoid using invasive plants in gardens and landscaping.
- Purchase non-invasive plants from reputable suppliers. When gardening, consider the use of native plants which provide habitat and food sources for wildlife.
- Do not dispose of invasive plants in the compost pile – discard them in the regular garbage or check with your municipality for disposal information.
- When hiking, prevent the spread of invasive plants and seeds by staying on trails and keeping pets on a leash.
- If you find Japanese knotweed or other invasive species in the wild, please contact the Invading Species Hotline at 1-800-563-7711, or report a sighting online.
- Ontario Invasive Plant Council
- Invasive Species: A Threat to Ontario’s Biodiversity
- Ontario Ministry of Agriculture, Food and Rural Affairs – Ontario Weeds
- Invasive Species Centre
OFAH/OMNR Invading Species Awareness Program. (2012). Japanese Knotweed. Retrieved from: http://www.invadingspecies.com. This factsheet may be reproduced for non-commercial purposes.
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