What is an Invasive Species?
Under the Invasive Species Act of Ontario (2015) an invasive species is defined as:
‘a species that is not native to Ontario, or to part of Ontario and is harming the natural environment of Ontario or of the part of Ontario in which it is present or is likely to harm the natural environment of Ontario or of a part of Ontario, regardless of whether it is present in Ontario or in a part of Ontario.’
The purpose of the Invasive Species Act is to reduce the introduction, spread, or impact these non-native species are having on Ontario’s native vegetation.
What is a Noxious Species?
Noxious species have the same negative impact on the environment that invasive species have. However, noxious species can be native to Ontario. A noxious species is designated by the appropriate regulating body as a species that causes harm to the surrounding environment. This could include humans, agriculture, livestock, etc. An invasive species can also be considered noxious, generally multiplying rapidly and very difficult to control. The Weed Control Act regulates noxious species and was created for the purpose of protecting agricultural practices.
The Confusion
The Invasive Species Act provides a multitude of species that are considered prohibited or restricted in Ontario. Some of the invasive species listed under the Act can be confused for native species in Ontario.
For example, the Invasive Species Act lists giant hogweed (Heracleum mantegazzianum) as an invasive species in Ontario. However, giant hogweed is commonly mistaken for its native relative cow parsnip (Heracieum maximum) which is not considered invasive or noxious. Furthermore, cow parsnip is not to be confused with wild parsnip (Pastinaca sativa L.) a noxious and invasive weed in Ontario. Confusing.... we know!
Identifying Giant Hogweed
Giant hogweed is part of the carrot family and considered a short-lived perennial. The easiest way to distinguish giant hogweed is by its height, stem colour, leaf size, and stem texture. Compared to its relative cow parsnip, giant hogweed is much larger, reaching a mature height of anywhere from 3 to 4.6 metres tall. The stem can range from dark purple to green or blotches of both colours. The stem contains ‘pimples’ with hairs emerging from them, giving a bumpy texture and appearance. Finally, the leaves can reach 1.5 metres in lenght.
Photos from: Oregon Department of Agriculture (ODA), Noxious Weed Control Program (2014).
Identifying Cow Parsnip
Cow parsnip has a similar leaf shape and flower structure to giant hogweed. However, cow parsnip only reaches a mature height of 2.4 metres tall. The stem is green but can appear to have a purple haze. The purple haze comes from a multitude of white fuzzy hairs on top of the thick ridged stem, creating the purple illusion.
Photos from: Oregon Department of Agriculture (ODA), Noxious Weed Control Program (2014).
Identifying Wild Parsnip
Wild parsnip is easily distinguishable from giant hogweed and cow parsnip by its flowers. Wild parsnip have yellow flowers while the other two species have white flowers. Wild parsnip only grows up to 1.5 metres tall. The stem is green to sometimes reddish and smooth with fewer hairs than cow parsnip. Wild parsnip does not have the purple haze often seen on cow parsnip.
Photos from the University of Illinois Extension, Kendall County Staff (top), Emily Swihart, University of Illinois Extension (bottom).
What's the Danger?
Why should you care? Besides the impact invasive and noxious species have on the environment, giant hogweed, cow parsnip, and wild parsnip can cause ill effects to the human body.
Wild parsnip is sometimes referred to as poison parsnip because it contains sap with harsh chemicals. The chemicals can cause photosensitivity on human skin leading to burns, rashes, and/or blisters. Giant hogweed has the same effect as wild parsnip when its sap comes in contact with human skin. Wild parsnip and giant hogweed have been observed to cause severe reactions. Cow parsnip can cause the same photosensitive reaction, but usually to a much lesser extent than the other two parsnips.
FRi’s encounter with cow parsnip in Northern Ontario
Proper disposal techniques should be consulted prior to removing the species. Removing the species improperly can lead to further dispersal or harmful reactions to the skin. If you are unsure of what species is present on your property, refrain from touching the plant with bare skin until its identity can be confirmed.
Species descriptions modified from the Ministry of Natural Resources’ webpage on Wild Parsnip and Oregon Department of Agriculture (ODA), Noxious Weed Control Program (2014).