Giant hogweed (Heracleum mantegazzianum)

Giant hogweed Common Names: Giant cow parsley

Description: This species has been listed as a noxious weed under federal law and is also prohibited under Michigan law.

Habit: Extremely tall (2.5-6 m, 8-20 ft) biennial or short-lived perennial with a deep (40-65 cm, 16-26 in) tap root.

Leaves: Alternate, large- up to 1.5 m (5 ft) wide; deeply divided and dissected leaves; hairy beneath; leaf stalk enlarged and surrounding the stem; upper leaves gradually becoming smaller.

Stems: Thick; 5-10 cm (2-4 in) in diameter; hollow; purple-mottled; with coarse white hairs.

Flowers: Small, white in color, clustered into large, slightly curved umbels at the top of each stem, typically bloom once and then die (robust biennial or monocarpic perennial); blooms June through July.

Fruit and seeds: Seeds in flat, dry, oval pods; 8-15 mm in length; one plant can produce up to 100,000 seeds.

Habitat: Native to Asia, now prefers open, moderately moist, cool sites but can be found in a range of habitats.

Reproduction: By seed or by re-sprouts from cut stumps.

Similar species: Cow parsnip (Heracleum maximum) is smaller (up to 8 ft tall), has dense fine white hairs under leaves and lacks purple mottling on stem; Angelica has smooth, sometimes purplish stems but lacks mottling and hairs.

Monitoring and rapid response: Monitor riparian sites and disturbed edge habitat in partial shade. Sap causes increased photosensitivity; may cause severe burns, blistering, dermatitis and dark scars, and even blindness; protect skin; mowing stimulates budding from the rootstalk; plants may be dug out, remove entire root, Research herbicide options as not all are effective. As this species has a limited distribution in Michigan, it is important to document new occurrences. Please obtain flowering or fruiting specimens and submit to: Anton Reznicek, Curator (Vascular Plants), University of Michigan Herbarium, 3600 Varsity Drive, Ann Arbor, MI 48108-2287.

Credits: The Michigan Natural Features Inventory (MNFI) has partnered with MISIN to provide the information in this fact sheet. Species images and/or information were used with permission from "A Field Identification Guide to Invasive Plants in Michigan's Natural Communities" and "A Field Guide to Invasive Plants of Aquatic and Wetland Habitats for Michigan.


Common Name:

Giant hogweed

Scientific Name:

Heracleum mantegazzianum

Family:

Apiaceae
(Carrot)

Duration:

Perennial

Habit:

Herbs

USDA Symbol:

HEMA17
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