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Giant Hogweed Identification
Giant hogweed (Heracleum mantegazzium)
Oregon "A" Designated Noxious Weed
Giant hogweed, Heracleum mantegazzianum, is a robust biennial or short-lived perennial of the carrot family. It is often confused with other more common weeds and native plants in the carrot family. For example, cow parsnip, poison hemlock and wild carrot. The primary characteristics that distinguish giant hogweed are plant height, stem color, stem texture and leaf size. Giant hogweed can reach a mature height of 10-15 feet. The stem is often dark purple in color, but can vary from entirely purple to mostly green with purple blotches. A key-defining characteristic is the texture of the stem, which is rough and bumpy in appearance. The stem is covered with blistery pimples with individual hairs emerging from each bump. Leaf size of the mature plant can also help distinguish this plant; leaves are up to 5 feet in length. Other notable characteristics, flowers are large white compound umbels up to 2 feet across, compound leaves are deeply divided into lobed toothed leaflets, and stems are hollow 2-4 inches in diameter.
Additional Information Links
ODA Giant Hogweed Profile
WeedMapper Profile and Maps  

  Giant Hogweed

Heracleum mantegazzianum

Cow Parsnip

Heracleum maximum

  Poison Hemlock

Conium maculatum


Giant Hogweed Plant
Cow Parsnip Plant
Poison Hemlock Plant
  Maximum height 10-15 feet. 
  Maximum height 8 feet.   Grows to be 3 - 10 feet tall.


 Giant Hogweed StemCow Parsnip Stem
Poison Hemlock Stem
  Thick hollow stalks are purplish, each purple spot surrounds a raised blister-based hair. Thick, ridged stem with fine white fuzzy hairs appears to have a purple haze. Smooth, hairless purple-spotted hollow stems.


 Giant Hogweed LeafCow Parsnip Leaf
Poison Hemlock Leaf
 Compound leaves deeply divided into lobed toothed leaflet. Divided into 3 segments, leaflets coarsely toothed, broad wing at the base of the leaf stalk.
Leaves are up to 12 inches in length and 4 inches wide. Each leaf is made up of several pairs of leaflets that sprout from opposite sides of a main leaf stalk. 


Giant Hogweed Flower
 Cow Parsnip FlowerPoison Hemlock Flower

  Up to 2 feet in diameter.  Has 6-10 inch flat clusters.  Grows with 2-3 inch flat clusters.