Family: Apiaceae (Carrot Family)
Duration and Habit: Biennial, Perennial Herb
Giant hogweed is a biennial or perennial herb in the carrot family (Apiaceae), growing 15 to 20 feet in height with stout dark reddish-purple stems and spotted leaf stalks. Hollow stalks and stem produce sturdy bristles. The compound leaves with three leaflets may expand to five feet in breadth.
WARNING: Do not touch or handle. Causes severe burning/blistering.
Native Lookalikes: Giant hogweed is often confused with cow parsnip (a.k.a. cow parsley) which is a native species. Cow parsnip Heracleum maximum belongs to the same genus a giant hogweed, and both plants produce caustic materials that can cause skin irritation which can lead to misidentification. Cow Parsnip is found throughout Texas. It has stalks are about 1 inch in diameter and solid green, while hogweed stalks can be 2.5 inches in diameter and are mottled with reddish spots, just like another member of the carrot family, poison hemlock.
One of the best ways to tell the difference is to look at the plant stems. The stem of cow parsnip does not contain the purple blotches that are found on giant hogweed.
A great side-by-side reference can be found
Ecological Threat: Giant Hogweed is an aggressive competitor. Because of its size and rapid growth, it
out-competes native plant species, reducing the amount of suitable habitat available for wildlife. Giant Hogweed dies back during the winter months, leaving bare ground that can lead to an increase in soil erosion on riverbanks and steep slopes.
Giant Hogweed contains a substance within its sap that makes the skin sensitive to ultra violet light. This can result in severe burns to the affected areas, producing swelling and severe, painful blistering. Large, watery blisters usually appear 15 to 20 hours after contact with the sap and sunlight. Contact between the skin and the sap of this species occurs either through brushing against the bristles on the stem (as with a stinging nettle) or breaking the stem/leaves. In the event of contact with the sap of this plant, the skin should be covered to reduce the exposure to sunlight and washed IMMEDIATELY and thoroughly with soap and water.
Biology & Spread: Flowers are made up of 50-150 flower rays with small, white florets, that form into an umbrella-shaped flower. Each flower can grow up to 2-1/2 feet in diameter. Each flower ray produce large elliptic dry fruits marked with brown swollen resin canals up to 1 mm in diameter. It flowers from mid-June to mid-July and then produces large flattened elliptic dry seeds with approximately 1500 seeds per flower head.
History: Giant hogweed was introduced from Eurasia around 1917 for use as an ornamental plant.
U.S. Habitat: Giant hogweed can invade a variety of habitats but prefers moist, disturbed soils such as riverbanks, ditches and railroad right-of-ways.
U.S. Nativity: Introduced to U.S.
Native Origin: Caucasus (Bailey, L.H. and E.Z. Bailey, Hortus Third: A Concise Dictionary of Plants Cultivated in the United States and Canada, MacMillan Publishing Co., Inc., New York , (1977).); NatureServe Explorer
U.S. Present: ME, MI, NY, PA, WA
If you believe you have found a giant hogweed, please report this species.
Distribution in Texas:
Joe Pye weed (Eupatorium dubium or fistulosum), boneset or white snake root (Eupatorium perfoliatum or rugosum), elderberry (Sambucus canadensis), southern arrowwood (Viburnum dentatum)
Do not cultivate, plant, purchase, or transplant this plant. It is very difficult to control. If found, notify your state Department of Agriculture, who will handle control measures. Use protective clothing, gloves and face visor or similar to undertake any cutting or removal of this species.
Manual: WARNING: Do not touch or handle without protection. Causes severe burning/blistering. Clear above ground leaf and stem material by hand; remove ground material of roots and seeds.
Chemical: It can be effectively controlled using any of several readily available general use herbicides such as glyphosate early in the season when leaves are less than two feet tall and before the plant flowers and sets seed. Follow label and state requirements.
Biocontrol: Cattle and pigs are cited as possible biocontrol agents. Both eat giant hogweed without apparent harm. Trampling also damages the plant.
Swearingen, J., K. Reshetiloff, B. Slattery, and S. Zwicker. 2002. Plant Invaders of Mid-Atlantic Natural Areas. National Park Service and U.S. Fish & Wildlife Service, 82 pp.
www.forestimages.org, http://plants.usda.gov, www.nps.gov/plants/alien,
Google Search: Heracleum mantegazzianum
Google Images: Heracleum mantegazzianum
NatureServe Explorer: Heracleum mantegazzianum
USDA Plants: Heracleum mantegazzianum
Invasive Plant Atlas of the United States: Heracleum mantegazzianum
Bugwood Network Images: Heracleum mantegazzianum