Giant Hogweed

(Click on an image below to see the captioned full-size version)
Figure 1		Figure 2		Figure 3		Figure 4		Figure 5		Figure 6
Figure 7		Figure 8		Figure 9

Scientific Name: Heracleum mantegazzianum
Common Names: Giant hogweed, Giant cow parsnip

CAUTION:
The clear, watery sap of giant hogweed contains toxins that cause phytophotodermatitis.
Skin coated with this sap becomes sensitive to sunlight leading to painful, burning blisters.
For more information see the article "Vegetation, Vegetables, and Vesicles: Plants and Skin" by Frances Northall http://www.nursing-standard.co.uk/archives/en_pdfs/envol11-03/env11n3p1823.pdf

Habitat:
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 form the large, tuberous roots that store much of the plant’s energy. (Figure 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:
Cow parsnip (Heracleum maximum), angelica (Angelica atropurpurea), wild chervil (Anthriscus sylvestris), poison hemlock (Conium maculatum), Queen Anne’s lace (Daucus carota), Golden Alexanders (Zizia aurea)

The following websites contain photos and descriptions of giant hogweed and similar species:
Massachusetts Department of Agricultural Resources
http://www.mass.gov/agr/pestalert/giant_hogweed_photos.htm

Giant Hogweed Comparison Table from IPANE
http://nbii-nin.ciesin.columbia.edu/ipane/ipanespecies/comparisontable.htm

Weed Website at Penn State University
http://weeds.cas.psu.edu/hogweed.pdf

Fact sheets and references:
Massachusetts Department of Agricultural Resources Pest Alert
http://www.mass.gov/agr/pestalert/giant_hogweed.htm

Massachusetts Giant Hogweed Wanted Poster
http://massnrc.org/pests/linkeddocuments/GHW.pdf

Status of Giant Hogweed populations in Massachusetts
http://massnrc.org/pests/pestFAQsheets/hogweed/giant_hogweed.htm

Cooperative Agricultural Pest Survey Giant Hogweed Page
http://www.ceris.purdue.edu/napis/pests/ghw/index.html

APHIS Giant Hogweed Fact sheet
http://www.aphis.usda.gov/lpa/pubs/fsheet_faq_notice/fs_phhgweed.pdf

Invasive Plant Atlas of New England
hhttp://nbii-nin.ciesin.columbia.edu/ipane/icat/browse.do?specieId=113

University of Connecticut
http://www.hort.uconn.edu/cipwg/giant_hogweed.html

Washington State Noxious Weed Control Board
http://www.nwcb.wa.gov/weed_info/Written_findings/Heracleum_mantegazzianum.html

The Perils of Giant Hogweed- Washington State University
http://gardening.wsu.edu/column/07-05-98.htm

The Giant Hogweed Best Practice Manual
http://www.giant-alien.dk/manual.html

The Infamous Giant Hogweed- Purdue University Extension
http://www.btny.purdue.edu/weedscience/2004/articles/gianthogweed04.pdf

last updated June 18, 2009