Giant Hogweed – Heracleum mantegazzianum

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June 1, 2012

Heracleum mantegazzianum

Apiaceae (Carrot family)

Proper identification will go a long way to alleviate worry about exposure and removal. Click "Download File" for a good, pictorial description of giant hogweed and look-alike species; Michigan State University Extension bulletin E-2935, “Giant Hogweed: An attractive but dangerous federal noxious weed.” 

Basic Information- For more details download the file

Life cycle

Giant hogweed is a biennial or perennial herb.

Leaves

Alternating leaves have deep irregular lobes and coarse, sharp teeth on the margins.  Leaves are very large—up to 5 feet across.

Stems

The stems are hollow with coarse white hairs that are noticeable at the node and base of the petiole.  They are green in color with purple blotches or specks.  Stems are 2 to 4 inches in diameter and can grow up to 12 to 15 feet.

Flowers and fruit

The flower is arranged as a compound umbel with many tiny white flowers.  Umbels can be 2.5 feet wide.  In Michigan the plant flowers from June to August.

Seeds

Mature seed from the current year is dormant and will not germinate until the following spring.  Seeds can remain viable in the soil for several years.

Toxicity

The plant exudes a clear sap that causes photodermatitis, a severe skin reaction.  Exposed skin will become highly sensitive to sunlight within 24-48 hours.  This may result in painful, burning blisters and red blotches that later develop into purple or blackened scars.  Wash immediately with soap and water if skin exposure occurs.

Photo credits:  Shiawassee Conservation District

Giant hogweed leaf
Giant hogweed leaf
Giant hogweed leaf
Giant hogweed leaf
Giant hogweed flower
Giant hogweed flower
Giant hogweed flower
Giant hogweed flower
Giant hogweed stem
Giant hogweed stem
Giant hogweed plant
Giant hogweed plant

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Tags: msu plant & pest diagnostics, toxic plants


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