Photo Credit: Thomas Denholm, New Jersey Department of Agriculture. Retrieved from Bugwood.org (Image Number: 2121076), used under CC BY 3.0 US, modified from the original
Common Name: Giant Hogweed
Scientific Name: Heracleum mantegazzianum
Habitat: forests - open areas, forests - wet areas, ditches
Provincial Designation: Prohibited Noxious
Prohibited Noxious weeds are plant species designated in the Alberta Weed Control Act. Prohibited noxious weeds must be destroyed when found, meaning all growing parts need to be killed or the plant's reproductive mechanisms need to be rendered non-viable.
Giant hogweed is native to the Caucasus and was introduced to North America. It was used as an ornamental garden plant and its seeds were used in cooking.
It can out-compete native plants in moist and wet areas and poses a human health concern. Giant hogweed's sap sensitizes skin to UV radiation and upon exposure can cause painful burns and blisters that may lead to hospitalization.
The single white flowers have 5 petals and are 5-15 mm wide. They are arranged in compound umbels with rounded tops up to 1 m diameter. Each compound umbel has more than 50 umbel stalks.
The leaves are huge and can grow up to 3 m in diameter. The leaf is palmate (like a hand) or pinnate (leaflets coming off a single stalk). The leaflets have lobed and/or serrated edges.
The thick stem is hollow with red blotches and stiff hairs. Giant hogweed is an impressive and uniquely large plant that grows up to 6 meters tall.
Can Be Confused With ...
Cow Parsnip - Heracleum maximum - Native species, much smaller than giant hogweed. All reports of giant hogweed in Edmonton have proven to be cow parsnip.
Queen Anne’s Lace - Daucus carota - Introduced but not a noxious species, much smaller and daintier than giant hogweed, also known as “wild carrot” - more often on dry land than wet.
Water Hemlock - Cicuta maculata - Native species, poisonous, leaves sometimes double compound (one stalk splits into leaflets, which then split again), flowers are much daintier than giant hogweed, and plant is smaller.
Learn more about this species:
See Fact Sheet - Alberta Invasive Species Council