Introduced Pests Outreach Project

Giant Hogweed

(Click on an image below to see the captioned full-size version)
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Scientific Name: Heracleum mantegazzianum
Common Names: Giant hogweed, Giant cow parsnip

Avoid direct contact with this plant! The clear, watery sap of giant hogweed contains toxins that cause phytophotodermatitis. Skin coated with this sap can become sensitive to sunlight and develop painful, burning blisters.

Disturbed habitats, roadsides, vacant lots, and along streams and rivers. It prefers rich, moist soil, in semi-shade conditions.

Key ID Features (Adults):
Biennial or perennial herb reaching 10-15 feet in height. (Figure 1)
Seedlings emerge in early spring. Leaves also arise from the large, tuberous roots that store much of the plant’s energy. (Fig. 2)
Stem is hollow, 2-4 inches in diameter, and covered with dark reddish-purple splotches and coarse hairs. (Figures 3 and 4)
Leaves are compound with three deeply incised leaflets. Leaves may reach up to 5 feet in width. (Figure 5)
Undersides of leaves look smooth and scaly. If hairs are present, they are coarse and white. A similar species, cow parsnip, has leaves that look fuzzy on the underside. (Figures 6 and 7)
White flowers appear mid-May through July. Flower heads are umbrella-shaped with a flat top and may reach 2 ½ feet in diameter. (Figure 8)
Fruits are dry and elliptical (1/4” – ¾” length by 1/8” –3/8” in width) marked with 3-5 brown swollen resin canals (1mm in diameter). (Figure 9)

Similar species:
Giant hogweed looks similar to many other species in the carrot family (Apiaceae). Species confused with giant hogweed include Cow parsnip (Heracleum maximum), angelica (Angelica atropurpurea), wild parsnip (Pastinaca sativa), wild chervil (Anthriscus sylvestris), poison hemlock (Conium maculatum), Queen Anne’s lace (Daucus carota), and Golden Alexanders (Zizia aurea)

Similar species comparison tools:
Fact sheets and references:

last updated June 19, 2018

Massachusetts Department of Agricultural Resources
Massachusetts Introduced Pests Outreach Project is a collaboration between the Massachusetts Dept. of Agricultural Resources and the UMass Extension Agriculture and Landscape Program. This website was made possible, in part, by a Cooperative Agreement from the United States Department of Agriculture's Animal and Plant Health Inspection Service (APHIS). It may not necessarily express APHIS' views.