Giant Hogweed, Heracleum mantegazzianum

Identification Information

Giant Hogweed is found sporadically throughout Maine, but is not a common plant. Giant hogweed is noteworthy because its sap causes severe skin irritation. When susceptible people come in contact with the sap and the skin is exposed to sunlight painful blisters develop. Giant Hogweed Control and Safety Information

Several plants are often confused with giant hogweed; it is important to accurately identify plants before taking actions.

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Is it Giant Hogweed?

Plant Name

Plant Picture

Leaf

Stem

Flower

Giant Hogweed, Heracleum mantegazzianum
Giant Hogweed Plant
Giant Hogweed leaf
Giant Hogweed Stem
Giant Hogweed Flower
Plants taller than 8 feet
Unevenly lobed leaves, up to 5 feet across
Green stems with purple blotches. Stems are 2-4 inches wide and hollow with rigid hairs
White flower clusters that appear in late June and July. Flowers are similar to queen-Anne’s-lace, but much larger, up to 2 feet across.
Toxic Properties: Clear watery sap has toxins that cause photo dermatitis. Skin contact followed by exposure to sunlight produces painful, burning blisters that may leave purple or black scars. Eye contact can cause temporary or permanent blindness. Control and Safety Information

Giant Hogweed Look-a-Likes

Plant Name

Plant

Leaf

Stem

Flower

Cow Parsnip, Heracleum maximum Cow Parsnip Plant Cow Parsnip Leaf Cow Parsnip Stem Cow Parsnip Flower
Plants are 5 to 8 feet tall, can cause a blistery rash in sensitive individuals Leaves are 2 to 2 1/2 feet and covered in soft hairs that may give a velvety appearance Deeply ridged stems maybe green or slightly purple and 1 to 2 inches in diameter. Hairs are fine, soft and fuzzy Flowers several weeks before giant hogweed. Flower clusters are up to 1 foot across.
Toxic Properties:The sap from Cow Parsnip leaves and stems may sensitize the skin so that it is very easily sunburned. Washing off the sap and wearing long sleeves for a few days apparently is the ticket after exposure. Management recommendations NYDOT
Water Hemlock, Cicuta maculata Water Hemlock Height Water Hemlock Leaves Water Hemlock Stem Water Hemlock Flower
Plants are 3 to 6 feet tall, and all plant parts are poisonous
Leaflets are up to 4 inches long and 1 1/4 inches wide with sharp pointed teeth and veins that end in each notch Stems are many branched and may be green or purple, or have purple streaks or spots Flowers are white umbels up to 6 inches across with 12 - 15 groups of umbellets with 10 or more in each cluster
Toxic Properties: A native plant and all parts can be deadly! The seedlings, seed heads and roots are most deadly. Contact poison control center and obtain emergency medical assistance as soon as possible. Poisoning symptoms include severe seizures and convulsions. One of the most toxic plants native to the United States. Management recommendations UNCE (PDF)
Angelica, Angelica atropurpurea Angelica Plant Angelica Leaf Angelica Stem Angelica Flower
Less than 8 feet tall Compound leaves can reach 2 feet wide and have dozen of small leaflets Waxy green to purple, smooth, hollow stems, 1 to 2 1/2 inches in diameter Softball size clusters of white or greenish white flowers, less then 1 foot in diameter
Toxic Properties: Angelica has long been used as a medicinal herb and is far less likely to cause a skin reaction than it's more toxic cousins. Cultivation and management Michigan State University (PDF)
Queen-Anne's Lace, Daucus carota Field of Queen-Anne's Lace Queen-Anne's Lace leaf Queen-Anne's Lace stem Queen-Anne's Lace flower
Plants are 1 to 4 feet tall Lacy, fern-like leaves Slender, hairy, hollow, green stems Small white flowers in a flat cluster 3 to 4 inches wide from May to October
Toxic Properties: Contact with sap can cause dermatitis reaction which is aggravated by exposure to sun. Management recommendations Minnesota DNR
Poison Hemlock, Conium maculatum Poison hemlock plant Poison hemlock leaf Poison hemlock stem Poison hemlock flowers
Plants are 4 to 9 feet tall. Bright green fern-like leaves, maybe glossy Smooth, waxy stems with purple blotches Small white flowers in numerous flat topped clusters on all branches
Toxic Properties: An introduced plant and all parts can be deadly! Seeds contain highest concentration of poison, are often mistaken for caraway. Can cause toxic reactions when inhaled. Human deaths have occurred from consuming roots, being mistaken for wild carrots or parsnips. In ancient Greece, it was used to poison political prisoners. Socrates drank the poisonous juice to commit suicide. Native Americans once used hemlock to poison tips of arrows. Management recommendations USDA-Forest Service (PDF).
Wild Parsnip, Pastinaca sativa Field of Wild Parsnip Wild Parsnip Leaf Wild parnsip stem Wild Parsnip Flower
Plants are 2 to 5 feet tall Compound leaves with a main stem with 5 to 15 leaflets Grooved, hollow stems Yellow flowers
Toxic Properties: It produces sap containing chemicals that can cause human skin to react to sunlight, resulting in intense burns, rashes or blisters. BMPs- Ontario Invasive Plant Council (PDF) and Ontario's Invading Species Awareness Program
Wild Lettuce, Lactuca sp. Wild Lettuce Plant Wild Lettuce Leaf Wild Lettuce Stem Wild Lettuce Flower
Plants are up to 6 feet tall Leaves are arranged alternately on stem and are 2 times longer than wide Stems may be slightly purple Small dandelion-like flowers
Toxic Properties: Contact with sap can cause dermatitis reaction which is aggravated by exposure to sun. Management recommendations Ontario Ministry of Agriculture, Food and Rural Affairs
Valerian, Valeriana officinalis Valerian Plant Valerian Leaf Valerian Stem Valerian Flowers
Plants are 3 to 5 feet tall Compound leaves with 7 to 10 pairs of toothed, lanced shaped leaflets Green stems White to pink flowers in July
Toxic Properties: Valerian root extracts can cause headache, excitability and insomnia in some people. It is also used as an herbal medicine to help with sleep disorders. Management recommendations USDA - FS (PDF)
Elderberry, Sambucus nigra ssp canadensis Elderberry Plant Elderberry Leaf Elderberry Twig Elderberry Flower
Woody shrub up to 12 feet tall Compound leaf, 6 to 11 inches long with 5 to 11 elliptical leaflets Stout, silvery to yellow-gray, woody twigs White flowers in flat topped cluster up to 8 inches across
Toxic Properties: Elderberries are edible but do contain alkaloids that can cause nausea in sensitive people. Management considerations USDA-FS

Image Citations, www.bugwood.org

Water Hemlock leaves and flowers, Janet Novak, Connecticut Botanical Society
Water Hemlock full plant for height, Peter M. Dziuk, Minnesota Wildflowers
Water Hemlock stems, U-Mass Extension
Angelica leaf and stem, Leslie Mehrhoff, University of Connecticut
Angelica plant and flower, www.wildplantdatabase.net
Queen Anne's lace plant, leaf and flower, Chris Evans, Illinois Wildlife Action Plan
Queen Anne's lace stem, Rob Routledge, Sault College
Poison hemlock, plant and flower, Pedro Tenorio-Lezama
Poison hemlock stem, Chris Evans, Illinois Wildlife Action Plan
Poison hemlock leaf, Robert Videcki, Doronicum Kft.
Wild parsnip leaf and stem, Ohio State Weed Lab Archive, The Ohio State University
Wild parsnip flower, John Cardini, The Ohio State University
Wild parsnip plant, Leslie Mehrhoff, University of Connecticut
Valerian plant, leaf, stem and flower, Leslie Mehrhoff, University of Connecticut
Elderberry plant, James H Miller, USDA Forest Service
Elderberry leaf, John Cardina, The Ohio State University
Elderberry stem, Rob Routledge, Sault College
Elderberry flower, Richard Webb