Giant Hogweed

The U.S. Department of Agriculture’s (USDA) Animal

and Plant Health Inspection Service (APHIS) regulates giant hogweed (Heracleum mantegazzianum)

as a noxious weed. This weed, which can be either

biennial or perennial, grows to a height between 8

and 15 feet. Giant hogweed often has a taproot but

can also have fibrous roots. It has hollow stems

between 2 and 4 inches in diameter with dark 

reddish–purple splotches and pustulate coarse white

hairs or bristles. The deeply incised compound

leaves grow up to 5 feet in width. Hairs on the underside of the leaf are stiff, dense, and stubby. The large

umbrella–shaped flower heads are up to 2 1/2 feet in

diameter across a flat top with numerous small 

flowers. The small flower appears from mid-May

through July. Giant hogweed produces flattened,

oval–shaped fruit with a broad, rounded base and

wide marginal ridges. This weed sprouts in the early

spring from the roots or seed.

Giant hogweed, which is native to the Caucasus,

has been introduced into Europe, Great Britain,

Canada, and the United States. Although it is listed

as a Federal noxious weed and is illegal to bring into

the United States or move across State lines, giant

hogweed is known to occur in New York,

Pennsylvania, and Washington. Reports of infestations have been received from Maine, Michigan, and

Washington, DC. This weed has been planted as an

ornamental in the United States and may have also

been brought into this country for its fruit, used as a

spice (golmar) in Iranian cooking.

Giant hogweed is likely to naturalize in many of

the places where it has been first introduced. The

plants thrive in many habitats but do particularly well

where the soil has been disturbed, such as on wastelands, riverbanks, and along railroads. The weed

prefers moist soil and partial shade, and can quickly

dominate an area where the conditions are just right.

Both people and animals may have a sensitivity

toward the giant hogweed’s sap. Furocoumarins in

the sap can cause a skin reaction known as photodermatitis. When photodermatitis occurs in people,

their skin becomes sensitive to ultraviolet light in sun

light. This sensitivity can lead to long–lasting swelling

and blisters. Contact with the eyes can cause temporary and sometimes permanent blindness.

APHIS’ Federal noxious weed program is

designed to prevent the introduction into the United

States of nonindigenous invasive plants and to prevent the spread of newly introduced invasive plants

within the United States. Noxious weed activities

include exclusion, permitting, eradication of incipient

infestations, survey, data management, public education, and (in cooperation with other agencies) 

integrated management of introduced weeds, including biological control.

For more information on giant hogweed, contact

Dr. Alan Tasker, the Federal Noxious Weeds program

coordinator, at (301) 734–5708 or e-mail him at

Alan.V.Tasker@aphis.usda.gov 

Factsheet

 	
  
	  

APHIS

Figure: Heracleum mantegazzianum. A. Portion of leaf,

showing its large and compound nature; B. Portion of inflorescence (a compound umbel); C. Portion of umbel in

flower (A-C all 0.65x); D. Individual staminate flower from

lateral inflorescence, top view; E. Fruit (a schizocarp), side

and edge views; F. Mericarp, following dehiscence of

schizocarp (D-F all 2.5x).

Sources: A. French 2122, Oregon (NY); B-F. Dixen et al.

488, Denmark (MO).
United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture

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