Heracleum mantegazzianum

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Legend for Species Pages

Giant Hogweed

Heracleum mantegazzianum Sommier & Levier
  • Occurrence in Alberta – reported but unconfirmed
  • Alberta Invasive Species Council fact sheet – Yes[1]
  • Global Invasive Species Database – Yes[2]
  • NatureServe Rank – Medium
  • Haber, Upland – No
  • Haber, Wetland – No
  • CWF, Status & Invasive Range – Low to Moderate, BC, NB, ON
  • Alberta Revegetation Guidelines – No
  • The Nature Conservancy – No
  • CBCN – No
  • AB Weed – Prohibited Noxious

Remarks

Known in BC and Ontario. Giant hogweed is often confused with cow parsnip (Heracleum lanatum), a very common native in Alberta. Giant hogweed is much larger (up to 5 m high, as opposed to up to 3 m maximum), the leaves are more deeply lobed, and the leaf edges are more sharply serrated.

[3]Link to Youtube, Giant Hogweed Identification and Comparison with Cow Parsnip


Giant hogweed mostly colonizes disturbed sites but also invades and displaces native vegetation. Skin contact causes extreme photosensitivity and burns. Eye contact can cause temporary or even permanent blindness.

It flowers in it's third or forth (sometimes second) year, then dies. Dark reddish patches on stems and leaf petioles distinguish it from other species (which may have more diffuse, lighter, reddish patches). The fruits are also distinctive.

Plants are 3-4 (up to 5) m high, with flowering stems 40-100 (up to 150) mm wide.

Leaves are alternate, 1-2.5 m long, usually ternate, but sometimes 5-pinnate. Leaflets are deeply divided usually into more than 3 segments, and irregularly toothed. Petioles of lower leaflets are about 100 mm long, and shorter than those of the upper leaflets.

Hollow white hairs, liquid-filled when fresh, cover most of the foliage except for upper leaf surfaces.

Flower petals are variable in size; the outer ones of an umbellet are up to 20 mm long and notched.

Mature fruits are elliptical or ovate, 6-18 mm long, 4-10 mm wide, and 1 mm thick. (Fruits of the native species, H. maximum, differ in being notched at the end.)


[4]Link to Wikipedia, Heracleum mantegazzianum, - "...Superficially, it resembles common hogweed (Heracleum sphondylium), Heracleum sosnowskyi or garden angelica (Angelica archangelica). It is phototoxic and considered to be a noxious weed in many jurisdictions. Giant hogweed is native to the Caucasus Region and Central Asia. It was introduced to Britain as an ornamental in the 19th century, and it has also spread to many other parts of Europe, the United States and Canada..."

[5]Link to USDA Plants profile for Heracleum mantegazzianum Sommier & Levier, giant hogweed.

[6]Link to weedinfo.ca, Giant Hogweed, - "...Giant hogweed was introduced from Europe, presumably as an ornamental, and has escaped along roadsides, streambanks and waste areas in scattered localities in southern Ontario..."


Giant Hogweed. Photo: XID Services
Reddish-purple blotches and stiff hairs on stem of Giant Hogweed. Photo: XID Services
Leaves of Giant Hogweed: large, deeply incised, and sometimes with more than 3 leaflets, unlike Cow Parsnip. Photo: XID Services
Cow Parsnip. Photo: Christine Messom
Cow Parsnip. Photo: Christine Messom
Cow Parsnip. Photo Christine Messom

For more photos and comparisons of the two species see:

Cow parsnip, H. lanatum: [7] and Giant hogweed, H. mantegazzianum: [8]

References

Nicolas A. Page, Ronald E. Wall, Stephen J. Darbyshire, and Gerald Mulligan, The Biology of Invasive Alien Plants in Canada. 4. Canadian Journal of Plant Science. December 2005