7. Giant hogweed (Heracleum mantegazzianum)
Giant hogweed has been invading rural and urban settings in Canada since the late 1940s. It may have been introduced as an ornamental plant because of its impressive height and showy white flowers. Not only does it threaten native plants, it’s also known to be a serious health hazard for people. The plant’s watery sap contains photosensitizing compounds that can cause severe burns when exposed to skin and sunlight. Parks, conservation areas, cities, municipalities and public gardens have been working to eradicate giant hogweed. Homeowners are encouraged to do the same, but are advised to use extreme care when removing this invasive plant from their gardens.