Giant Hogweed (Heracleum mantegazzianum)

Giant Hogweed (Heracleum  mantegazzianum)

 

Giant Hogweed is generally found along roadsides, in ditches, along streambanks and in disturbed waste areas. The clear watery sap of Giant hogweed contains toxins that can cause severe dermatitis. UV radiation activates compounds in the sap resulting in severe burns when exposed to the sun. Symptoms occur within 48 hours and consist of painful blisters. Purplish scars may form that last for many years.

HISTORY

Giant Hogweed originates from Asia. It was introduced to North America as an ornamental garden plant. It is now found in many provinces through-out Canada, as well as a number of US states. There are only a couple of known sites on PEI, and all are contained within private gardens.

IDENTIFICATION

Giant Hogweed has a couple of look-a-likes that grow in PEI, including: cow parsnip and Queen Anne’s lace. Here are a few features you can use to positively identify Giant Hogweed:

  • Grows much taller than the look-a-likes at 5 m tall
  • Umbrella-shaped flowering portion can be 1.5m in diameter
  • Hollow stem covered with purple streaks and spots
  • Stems covered in coarse hairs
  • Many white flowers bloom in June-August
  • Leaves are deeply-lobed, have sharply-jagged edges and 3 leaflets
  • Seeds are oval-shaped with 4 dark lines
  • Giant Hogweed has several lookalikes on PEI, including the native Cow Parsnip (Heracleum maximum) and fellow invasive, Woodland Angelica (Angelica sylvestris)

PEIISC factsheet on Giant Hogweed

Giant Hogweed is considered a priority species for the PEI Invasive Species Spotters Network. If you see this plant, please report your sighting.