Heracleum mantegazzianum, commonly known as giant hogweed, is a monocarpic perennial herbaceous flowering plant in the carrot family Apiaceae. H. mantegazzianum is also known as cartwheel-flower, giant cow parsley, giant cow parsnip, or hogsbane. In New Zealand, it is also sometimes called wild parsnip (not to be confused with Pastinaca sativa) or wild rhubarb.
Giant hogweed is native to the western Caucasus region of Eurasia. It was introduced to Britain as an ornamental plant in the 19th century, and has also spread to other areas in Western Europe, the United States, and Canada. Its close relatives, Sosnowsky's Hogweed and Persian hogweed, have similarly spread to other parts of Europe.
The sap of giant hogweed is phototoxic and causes phytophotodermatitis in humans, resulting in blisters and scars. These serious reactions are due to the furocoumarin derivatives in the leaves, roots, stems, flowers, and seeds of the plant. Consequently, it is considered to be a noxious weed in many jurisdictions.
Giant hogweed typically grows to heights of 3 to 4.5 m (9.8 to 14.8 ft). Under ideal conditions, a plant can reach a height of 5.5 m (18 ft). The leaves are incised and deeply lobed. A mature plant has huge leaves, between 1–1.5 m (3 ft 3 in–4 ft 11 in) wide, and a stout, bright green stem with extensive dark reddish-purple splotches and prominent coarse white hairs, especially at the base of the leaf stalk. Hollow, ridged stems vary from 3–8 cm (1.2–3.1 in) in diameter, occasionally up to 10 cm (3.9 in) in diameter and can grow to more than 4 m (13 ft) high. Dark red spots on the stem each surround a single hair.  The umbrella-shaped inflorescence, called a compound umbel, may be up to 100 cm (39 in) in diameter across its flat top. The flowers are white or greenish white and may be radially symmetrical or strongly bilaterally symmetrical (zygomorphic). The fruits are schizocarps, producing seeds in dry, flattened, oval pairs.:825 Each seed is approximately 1 cm (0.39 in) in length, with a broadly rounded base and broad marginal ridges, tan in color with brown lines (so-called oil tubes) extending 3/4 of the length of the seed.
The life cycle of giant hogweed consists of four phases:
- Pre-flowering plants: In the first year, leaves sprout from seed. In subsequent years, leaves sprout from overwintering roots as well as seeds. This pre-flowering phase continues for several years.
- Flowering plants (midsummer): After several years of growth, the plant flowers.
- Seeds (late summer/early autumn): A flowering plant produces 20,000 or more seeds.
- Dead stems (late autumn/winter): After producing seeds, the plant dies, leaving dried stems and seed heads standing.
During the first few years of growth, the leaves and stem of a pre-flowering plant die over the winter. In the spring, the plant grows back from its root. In other words, the giant hogweed is a herbaceous perennial.
A giant hogweed plant usually produces a flowering stalk in 3–5 years but plants may take up to 8 years to flower if conditions are unfavorable. In the Czech Republic, a single plant reached 12 years old before flowering. In any case, when the plant finally flowers, it does so between June and July.
Giant hogweed is a monocarpic perennial, that is, after a mature plant flowers and produces seed, the entire plant dies. During the following winter, tall dead stems mark the locations where the flowering plants once stood.
The seeds are dispersed short distances by wind but can travel longer distances by water, animals, and people. That said, the vast majority of seeds (95%) are found in the top 5 cm (2.0 in) of the soil within a few meters of the parent plant. Seeds may stay alive in the seed bank for more than five years.
A seed deposited in the seed bank is initially dormant. Dormancy is broken by the cold and wet conditions of fall and winter, and so freshly deposited seeds lay dormant until at least the following spring, at which time approximately 90% of the previously dormant seeds will germinate. The rest remain dormant in the seed bank.
Seeds normally result from cross-pollination between two or more plants but self-pollination is also possible. More than half the seeds produced by self-pollination will germinate and give rise to healthy seedlings. Hence a single isolated seed may give rise to a colony of new plants.
The various species of the Heracleum genus are similar in appearance with only minor differences. An outlier is H. mantegazzianum, the size of which is exceptional. The plant typically reaches 4 m (13 ft) high (and sometimes more than 5 m (16 ft) high) while the other species of the Heracleum genus rarely exceed 3 m (9.8 ft) high. There are considerable differences in the size of the umbel, leaves, and stem of H. mantegazzianum as well.
In North America, the native cow parsnip (H. maximum) is often mistaken for giant hogweed (H. mantegazzianum). Apart from overall size differences (which present themselves in the umbel, stem, and leaves), the two species closely resemble each other.
The following table compares Heracleum mantegazzianum and Heracleum maximum feature by feature:
|H. mantegazzianum||H. maximum|
|Height||Typically 3 to 4.5 m (9.8 to 14.8 ft) tall||Up to 2.5 m (8 ft 2 in) tall|
|Leaves||Compound, lobed leaves typically 100 cm (39 in) wide, up to 150 cm (59 in) wide; mature leaf has deep incisions and serrated edges||Compound, lobed leaves up to 60 cm (24 in); mature leaf is less incised with less jagged edges|
|Stem||Green stems from 3–8 cm (1.2–3.1 in) in diameter, occasionally up to 10 cm (3.9 in) in diameter, with dark reddish-purple splotches and coarse white hairs at the base of the leaf stalk||Green ridged stems up to 5 cm (2.0 in) in diameter with fine white hairs (no purple splotches)|
|Flowers||White umbel is typically 80 cm (31 in) in diameter, up to 100 cm (39 in) in diameter, with 50–150 flower rays per umbel; flowers bloom mid-June to mid-July||White umbel up to 30 cm (12 in) in diameter with 15–30 flower rays per umbel; flowers bloom late May to late June|
|Seeds||Oval-shaped seeds||Heart-shaped seeds|
Other plant species in the Apiaceae family have features similar to those of the giant hogweed (H. mantegazzianum):
- In Ontario, giant hogweed look-alikes include: cow parsnip (Heracleum maximum), wild parsnip (Pastinaca sativa), various angelica species (especially Angelica atropurpurea, the native purplestem angelica), and Queen Anne’s lace (Daucus carota)
- In New York State, giant hogweed look-alikes include: cow parsnip (Heracleum maximum), wild parsnip (Pastinaca sativa), angelica, and poison hemlock.
- In Europe, giant hogweed look-alikes include: hogweed (Heracleum sphondylium and Heracleum sphondylium ssp sibiricum), wild parsnip (Pastinaca sativa), garden angelica (Angelica archangelica), and wild angelica (Angelica sylvestris)
In Europe, over 20 species of the genus Heracleum have been recorded. Identification of Heracleum mantegazzianum is further complicated by the presence of two additional tall invasive hogweed species: Heracleum sosnowskyi and Heracleum persicum. Other than size (as mentioned above), these three species have very similar characteristics.
Heracleum mantegazzianum is native to the western Caucasus region of Eurasia. Because of its impressive size, giant hogweed was brought to Europe and North America as an ornamental plant and garden curiosity.
Migration to Europe
Heracleum mantegazzianum was first described in the scientific literature in 1895 but by that time more than a dozen European countries had already imported the plant as “an ornamental curiosity.” The introduction of Heracleum mantegazzianum was first recorded in Great Britain in 1817 when it was put on the seed list at the Kew Botanic Gardens in London. By 1828, the first natural population was recorded, growing wild in Cambridgeshire, England.
The spread of Heracleum mantegazzianum throughout Europe continued unabated until the middle of the 20th century, at which time the dangers of giant hogweed had become more widely known. Despite the warnings, however, the plant continued to be used by gardeners, beekeepers, and farmers (for cattle fodder) for another 50 years. Heracleum mantegazzianum was finally de-listed by the Royal Horticultural Society of Great Britain in 2002.
Migration to North America
During the 20th century, giant hogweed was transported to the United States and Canada for display in arboreta and Victorian gardens. The earliest recorded planting in North America was in 1917, in gardens near Highland Park in the city of Rochester, New York.
By 1950, giant hogweed had appeared in southern Ontario, and within a quarter century, the plant was firmly established in Ontario. It was first collected from Nova Scotia in 1980 and Quebec in 1990. Giant hogweed was still available for sale in Canadian nurseries as late as 2005.
On the west coast of North America, Heracleum mantegazzianum appeared in Oregon, Washington, and southwestern Canada but it is not clear how the species found its way into this region. First reports of giant hogweed in British Columbia were published in the 1930s.
Giant hogweed is now widespread throughout the British Isles, especially along riverbanks. By forming dense stands, they can displace native plants and reduce wildlife habitats. It has spread in the northeastern and northwestern United States, and southern Canada and is an invasive species in Germany, France, and Belgium; in sites where it has settled, it overtakes the local native species, Heracleum sphondylium.
In Canada, the plant has been sighted in British Columbia, Alberta, Saskatchewan, Ontario, Quebec, New Brunswick, Nova Scotia, and in isolated areas of Newfoundland. It has been seen in Quebec since the early 1990s. The plant's spread in Ontario began in the southwest and was seen in 2010 in the Greater Toronto Area and Renfrew County near Ottawa.
Giant hogweed now occurs in the west in British Columbia, Washington, and Oregon and in eastern North America from Newfoundland and Nova Scotia west to Ontario and Wisconsin and south to Indiana, Maryland, and New Jersey. It is also recorded occasionally in Michigan, and in June of 2018, it was reported growing in Virginia and North Carolina. The plant is a federally listed noxious weed in many US states.
Public health and safety
The sap of the giant hogweed plant is phototoxic. Contact with the plant sap prevents the skin from protecting itself from sunlight, which leads to phytophotodermatitis, a serious skin inflammation. A phototoxic reaction can begin as soon as 15 minutes after contact with the sap. Photosensitivity peaks between 30 minutes and two hours after contact but can last for several days.
Authorities advise that all humans (especially children) should stay away from giant hogweed. Protective clothing, including eye protection, should be worn when handling the plant. If you come in contact with the sap of the giant hogweed, immediately wash the affected area with soap and cold water and avoid further exposure to sunlight for at least 48 hours.
Because of its phototoxicity and invasive nature, giant hogweed is often actively removed.
The European Union funded the Giant Alien project to combat the plant.    On August 2, 2017, it added the species to its List of Invasive Alien Species of Union concern, thus placing restrictions on keeping, importing, selling, breeding and growing it and requiring governments to detect and eradicate it throughout the EU.
In the US, hogweed is regulated as a federal noxious weed by the US government, and is illegal to import into the United States or move interstate without a permit from the Department of Agriculture. The USDA Forest Service states pigs and cattle can eat it without apparent harm. The New York State Department of Environmental Conservation has had an active program to control giant hogweed since 2008. In 2011, Maine state horticulturists, describing the plant as "Queen Anne's lace on steroids", reported that it has been found at 21 different locations in Maine, with the number of plants ranging from one to a hundred.
In 1971, the progressive rock band Genesis released their third album Nursery Cryme, which includes the track "The Return of the Giant Hogweed." The song tells the story of the plant's introduction to Britain:
- Long ago in the Russian hills
- A Victorian explorer found the regal Hogweed by a marsh
- He captured it and brought it home...to London
- And made a present of the Hogweed
- To the Royal Gardens at Kew
The lyrics go on to goad the reader to "strike by night" since the invading plants "need the sun to photosensitize their venom," which demonstrates a fair appreciation for the mechanism of phytophotodermatitis.
- Heracleum, the genus
- Other tall invasive Heracleum species: Heracleum sosnowskyi and Heracleum persicum
- Non-invasive Heracleum species: Heracleum sphondylium and Heracleum maximum
- Species that can be mistaken for Heracleum mantegazzianum: wild parsnip, garden angelica, wild angelica
- List of poisonous plants
- "Heracleum mantegazzianum". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved 2013-08-06.
- "National Pest Plant Accord". Ministry for Primary Industries, Government of New Zealand. 2012. p. 70. Archived from the original on 4 February 2018.
- "Species Profile- Giant Hogweed (Heracleum mantegazzianum)". National Invasive Species Information Center, United States National Agricultural Library.
- Forney, Thomas; Miller, Glenn; Myers-Shenai Beth (27 May 2009). "Oregon Department of Agriculture Plant Pest Risk Assessment for Giant Hogweed Heracleum mantegazzianum" (PDF). Archived from the original (PDF) on 28 May 2010.
- "Giant Hogweed". Wild Food UK. Retrieved August 13, 2018.
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- Stace, C. A. (2010). New Flora of the British Isles (Third ed.). Cambridge, U.K.: Cambridge University Press. p. 450. ISBN 9780521707725.
- "Giant Hogweed Identification". New York State Department of Environmental Conservation. Retrieved September 6, 2018.
- Parnell, J. and Curtis, T. 2012. Webb's An Irish Flora. Cork University Press. ISBN 978-185918-4783
- "Beware Giant Hogweed!" (PDF). New York State Department of Environmental Conservation. Retrieved September 1, 2018.
- Booy, Olaf; Cock, Matthew; Eckstein, Lutz; Hansen, Steen Ole; Hattendorf, Jan; Hüls, Jörg; Jahodová, Sárka; Krinke, Lucás; Marovoková, Lanka; Müllerová, Jana; Nentwig, Wolfgang; Nielsen, Charlotte; Otte, Annette; Pergl, Jan; Perglová, Irena; Priekule, Ilze; Pusek, Petr; Ravn, Hans Peter; Thiele, Jan; Trybush, Sviatlana; Wittenberg, Rüdiger (2005). "The giant hogweed best practice manual: guidelines for the management and control of invasive weeds in Europe" (PDF). Hørsholm: Center for Skov, Landskab og Planlægning/Københavns Universitet. ISBN 87-7903-209-5. Retrieved September 1, 2018.
- Gucker, Corey L. (2009). "Heracleum mantegazzianum". Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Retrieved September 11, 2018.
- "Giant Hogweed Biology". New York State Department of Environmental Conservation. Retrieved September 1, 2018.
- Klingenstein, F. (2007). "NOBANIS – Invasive Alien Species Fact Sheet – Heracleum mantegazzianum" (PDF). Online Database of the North European and Baltic Network on Invasive Alien Species. NOBANIS. Retrieved September 17, 2018.
- O’Neill, Jr., Charles R. (February 2007). "Giant Hogweed (Heracleum mantegazzianum) - Poisonous Invader of the Northeast" (PDF). New York Sea Grant, SUNY College at Brockport. Retrieved September 18, 2018.
- "Giant hogweed information". NetRegs. U.K. Government. Archived from the original on 2007-02-23.
- "5 things you need to know about toxic hogweed". CBC News.
- Halfnight, Drew (July 13, 2010). "Giant weed that burns and blinds spreads across Canada". The National Post.
- "Plants profile for Heracleum mantegazzianum".
- "Giant hogweed: Not widely spread in Michigan".
- Diebel, Matthew (18 June 2018). "Giant Hogweed, a Plant That Can Cause Burns and Blindness, Found in Virginia". USA Today.
- Ducharme, Jamie (June 20, 2018). "A Giant Plant That Can Cause Blindness Was Spotted for the First Time in a New State". Time. New York.
- "Health Hazards & Safety Instructions for Giant Hogweed (with graphic photos)". New York State Department of Environmental Conservation. Retrieved September 3, 2018.
- "Giant Alien". Giant Alien Project, project no. EVK2-CT-2001-00128, European Union. Archived from the original on 2016-10-03.
- "GIANT ALIEN — Result In Brief". Retrieved 2018-07-04.
- "Giant Hogweed (Heracleum mantegazzianum) - A pernicious invasive weed: Developing a sustainable strategy for alien invasive plant management in Europe". Retrieved 2018-07-04.
- "List of Invasive Alien Species of Union concern". Retrieved 2018-07-04.
- Wildlife & Countryside Act 1981 Section 14 and Schedule 9, Part II.
- "Invasive and Noxious Weeds: Federal Noxious Weeds". Natural Resources Conservation Service. U.S. Department of Agriculture.
- "Giant Hogweed" (PDF). USDA Forest Service. June 20, 2005. Retrieved August 13, 2018.
- "NYSDEC Giant Hogweed Control Program". New Paltz, N.Y.: New York State Department of Environmental Conservation. Archived from the original on May 6, 2015.
- "State confirms poisonous plant sightings". The Portland Press Herald. May 22, 2012. Retrieved 2015-06-21.
|Wikispecies has information related to Heracleum mantegazzianum|
|Wikimedia Commons has media related to Heracleum mantegazzianum.|
- Giant Hogweed (Heracleum mantegazzianum): A Federal Noxious Weed U.S. Department of Agriculture
- "Giant Hogweed". the Ontario [Canada] Federation of Anglers & Hunters. Archived from the original on 2009-01-16.
- Identifying invasive plants: Japanese knotweed, giant hogweed and other invasive plants on NetRegs.gov.uk
- Photo of blisters caused by the plant (Graphic) from the Finnish Environment Institute (in Finnish) (archived February 6, 2012)
- Surveys for natural enemies of giant hogweed (Heracleum mantegazzianum) in the Caucasus region and assessment for their classical biological control potential in Europe
- "Beware Giant Hogweed!" brochure from New York State Department of Environmental Conservation
- "Giant Hogweed in Germany"
- "Photo bank: Heracleum mantegazzianum". Alien Species photo bank. NOBANIS. Retrieved September 20, 2018.