Written by: Tvisha Lakhani

Edited by: Yara

Designed by: Maahi Jain

Published by: Maryam Khan


     Giant hogweed is an invasive species found across North America. A member of the carrot family, its scientific name is heracleum mantegazzianum. It has a scattered distribution throughout southern and central Ontario. Also called the cartwheel flower, the plant generally has a thick stem peppered with small, coarse white hairs and dark red-purple specks. Giant hogweed sports wide leaves that are spiked on the ends. It blooms clusters of tiny white flowers, often in the shape of an upside-down bowl, as seen in the picture above. Giant hogweed can grow up to an immense height of up to 5 feet.

Originally, giant hogweed came from the Caucasus, a mountainous region close to the Caspian Sea and the Black Sea. It was likely brought to Canada as an ornamental plant in the 19th or early 20th century. In Canada, giant hogweed does not have any known natural predators, such as diseases or pests. This allows the species to quickly spread and invade areas.

While giant hogweed can grow in almost any environment, it is generally found in places with moist, nutrient-rich soil and lots of light. It is often seen along roadsides, ditches, streams, and in open fields and woodlands.

As an invasive species, giant hogweed is harmful to the ecosystem because it can compete with native plants. Due to its height, giant hogweed can ‘shade out’ certain plants, meaning it can block the sunlight from reaching shorter plants. This can hinder the growth of native plant species and consequently reduce biodiversity in the ecosystem.

Giant hogweed looks similar to other plants like Queen Anne’s lace and cow parsnip. However, if you suspect you see a giant hogweed plant, it is generally not wise to touch it for further inspection because it can be dangerous to humans and other animals. Giant hogweed has phototoxic sap that can severely burn skin if touched. Furanocoumarins are the main component of the sap that give it its burning sensation when exposed to sunlight. The sap is believed to even cause blindness if it gets into the eyes. When handling a giant hogweed plant, protective clothing like long sleeved shirts, eye protection, and waterproof gloves should always be worn. If you see giant hogweed on your property, you should hire a professional exterminator that can remove the plant safely without spreading large amounts of seeds. 

Currently, giant hogweed is listed as a noxious weed under the Ontario Weed Control Act. To report a sighting of giant hogweed or any other invasive species, please contact the Invading Species Hotline at 1-800-563-7711.




Works Cited

Giant Hogweed. (2021). Ontario’s Invading Species Awareness Program. http://www.invadingspecies.com/invaders/plants/giant-hogweed-2/

Giant Hogweed Poisoning in Dogs. (n.d.). Wag. https://wagwalking.com/condition/giant-hogweed-poisoning

Government of Ontario. (2022, August 2). Giant hogweed. Ontario. https://www.ontario.ca/page/giant-hogweed

Gvozdetsky, N. A., Bruk, S. I., Owen, L., Chauhan, Y., Goldberg, M., Parrott-Sheffer, C., Rodriguez, E., Singh, S., Tikkanen, A., Wallenfeldt, J., Young, G., & Editors of Encyclopaedia Britannica. (2023, March 15). Caucasus. Encyclopedia Britannica. https://www.britannica.com/place/Caucasus

Houshiar, A. (2015, June 12). Golpar | A Persian Spice. Fig & Quince. https://figandquince.com/golpar-angelica-spice-persian/

Invasive Species Centre. (n.d.). Giant Hogweed. https://invasivespeciescentre.ca/wp-content/uploads/2019/11/Giant-Hogweed-OFAH.pdf

Merbt, E. (2014). Hercules Herb Giant Hogweed [Photograph]. Pixabay. https://pixabay.com/photos/hercules-herb-giant-hogweed-hogweed-336224/

New York State Department of Environmental Conservation. (n.d.). Giant Hogweed. https://www.dec.ny.gov/animals/39809.html

NickyPe. (2021). Hogweed Seed Heads Seeds [Photograph]. Pixabay. https://pixabay.com/photos/hogweed-seed-heads-seeds-golpar-6567732/

Nottawasaga Valley Conservation Authority. (n.d.). Invasive Species Fact Sheet – Giant Hogweed. https://www.nvca.on.ca/Shared%20Documents/Giant%20Hogweed%20Fact%20Sheet.pdf

O’Neill, C. R., Jr. (2009, August). Giant Hogweed (Heracleum mantegazzianum) – Poisonous Invader of the Northeast. New York Sea Grant. https://seagrant.sunysb.edu/ais/pdfs/GiantHogweedFactsheet.pdf

Ontario Invasive Plant Council. (n.d.). Giant Hogweed. Invasive Species Centre. https://www.invasivespeciescentre.ca/invasive-species/meet-the-species/invasive-plants/giant-hogweed/

Ontario Ministry of Agriculture, Food and Rural Affairs. (n.d.). Noxious Weeds in Ontario. http://omafra.gov.on.ca/english/crops/facts/noxious_weeds.htm

Ontario Ministry of Agriculture, Food and Rural Affairs. (n.d.). Weeds Act – Frequently Asked Questions. http://omafra.gov.on.ca/english/crops/facts/faq_weeds_act.htm

Petruzzello, M. & Editors of Encylopaedia Britannica. (2015, July). Hogweed. Encyclopedia Britannica. https://www.britannica.com/plant/hogweed