Heracleum mantegazzianum

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Legend for Species Pages

[edit] Giant Hogweed

• Occurrence in Alberta – reported but unconfirmed
• Global Invasive Species Database – Yes[1]
• 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

[edit] Remarks

Known in BC, ON, similar to H. lanatum, a very common native in Alberta, but larger (up to 5 m high, as opposed to up to 3 m maximum). 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, are differ in being notched at the end.

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: [2] and Giant hogweed, H. mantegazzianum: [3]

[edit] 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