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 furanocoumarin 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 2 to 5 m (6 ft 7 in to 16 ft 5 in). Under ideal conditions, a plant can reach a height of 5.5 m (18 ft 1 in). 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 (1–3 in) in diameter, occasionally up to 10 cm (4 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 (3 ft 3 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 (1⁄2 in) in length, with a broadly rounded base and broad marginal ridges, tan in color with brown lines (so-called oil tubes) extending ¾ 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 eight years to flower if conditions are unfavorable. In the Czech Republic, a single plant reached twelve years old before flowering. In any case, when the plant finally flowers, it does so between June and July (in the northern hemisphere).
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. Most seeds (95%) are found in the top 5 cm (2 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 lie 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 genus Heracleum are similar in appearance, but vary in size. H. mantegazzianum is among the tallest, typically reaching 4 m (13 ft) high (and sometimes more than 5 m or 16 ft high), whereas Heracleum species native to Western Europe, such as ordinary Hogweed (H sphondlylium), or North America, such as the cow parsnip (H. maximum), rarely exceed 3 m (10 ft) high. There are considerable differences in the size of the umbel, leaves, and stem of H. mantegazzianum as well.
The following table compares Heracleum mantegazzianum and Heracleum maximum feature by feature:
|H. mantegazzianum||H. maximum|
|Height||Typically 3 to 4.5 m (9 ft 10 in to 14 ft 9 in) tall||Up to 2.5 m (8 ft 2 in) tall|
|Leaves||Compound, lobed leaves typically 100 cm (3 ft 3 in) wide, up to 150 cm (4 ft 11 in) wide; mature leaf has deep incisions and serrated edges||Compound, lobed leaves up to 60 cm (2 ft 0 in); mature leaf is less incised with less jagged edges|
|Stem||Green stems from 3–8 cm (1–3 in) in diameter, occasionally up to 10 cm (4 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 in) in diameter with fine white hairs (no purple splotches)|
|Flowers||White umbel is typically 80 cm (2 ft 7 in) in diameter, up to 100 cm (3 ft 3 in) in diameter, with 50–150 flower rays per umbel; flowers bloom mid-June to mid-July||White umbel up to 30 cm (1 ft) in diameter with 15–30 flower rays per umbel; flowers bloom late May to late June|
|Fruits||Oval-shaped fruits||Heart-shaped fruits|
Other plant species in the family Apiaceae have features somewhat similar to those of the giant hogweed (H. mantegazzianum). Examples:
- In Ontario: 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: cow parsnip (Heracleum maximum), wild parsnip (Pastinaca sativa), angelica, and poison hemlock.
- In Europe: hogweed (Heracleum sphondylium and Heracleum sphondylium ssp sibiricum), wild parsnip (Pastinaca sativa), garden angelica (Angelica archangelica), and wild angelica (Angelica sylvestris)
Many more species exist; in Europe, over 20 species are found of the genus Heracleum alone.
None of these reach a similar size, but many are phototoxic.
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 across Europe
Heracleum mantegazzianum was first described in 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 native to Russia and was further distributed during the late 1960s, later spreading extensively on its own throughout Russia and eastern Europe.
Giant hogweed is widespread throughout western and northern Europe, especially along terrains such as coastal areas and riverbanks. By forming dense stands, it 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 across western Europe; in sites where it has settled, it overtakes the local native species, Heracleum sphondylium.
In Canada, the plant occurs in most provinces, except in the prairies. 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.
In the United States, giant hogweed occurs in Maine, Wisconsin and south to Indiana, Michigan, Maryland, and New Jersey. In June 2018, it was reported growing in Virginia and North Carolina. The plant is federally listed as a noxious weed in many US states.
Giant hogweed is widespread in Russia and the Baltic states, and present in eastern Europe.
Public health and safety
The sap of the giant hogweed plant is phototoxic. Contact with the plant sap prevents the skin from being able to protect 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. Parts of the body that come into contact with the sap of giant hogweed should be immediately washed with soap and cold water, and further exposure to sunlight should be avoided for at least 48 hours. Other Heracleum species, such as the cow parsnip (Heracleum maximum), are likewise phototoxic, and hence similar caution is advised. Due to physical similarities to Queen Anne's lace, giant hogweed and its relatives are sometimes mistaken as harmless plants.
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 United Kingdom, the Wildlife and Countryside Act 1981 makes it an offence to plant or cause giant hogweed to grow in the wild.
In the United States, hogweed is regulated as a federal noxious weed by the U.S. 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 popular culture
The 1971 album Nursery Cryme by the progressive rock group Genesis contains a song called 'The Return of the Giant Hogweed'. The darkly-humorous lyrics describe an attack on the human race by Heracleum mantegazzianum, long after the plant was first 'captured' and brought to England by a Victorian explorer.
In Season 10 Episode 3 "Ghosts" (first aired October 20, 2019) of the AMC television series The Walking Dead, the character Aaron is attacked by "walkers" that have hogweed flowers growing from their decomposing bodies. Aaron comes into close contact with the hogweed, rendering him unable to properly see, and more susceptible to harm.
In her 1985 novel "Curse of the Giant Hogweed," popular mystery author Charlotte MacLeod places her established character Peter Shandy and his colleagues in a fantasy version of Wales to investigate Giant Hogweed endangering Britain's hedgerows.
- 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 (giant hogweed)". CABI. November 6, 2018. Retrieved December 8, 2018.
- "Heracleum mantegazzianum". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved August 6, 2013.
- "National Pest Plant Accord". Ministry for Primary Industries, Government of New Zealand. 2012. p. 70. Archived from the original on February 4, 2018.
- "Species Profile- Giant Hogweed (Heracleum mantegazzianum)". National Invasive Species Information Center, United States National Agricultural Library.
- Forney, Thomas; Miller, Glenn; Myers-Shenai Beth (May 27, 2009). "Oregon Department of Agriculture Plant Pest Risk Assessment for Giant Hogweed Heracleum mantegazzianum" (PDF). Archived from the original (PDF) on May 28, 2010.
- "Giant Hogweed". Wild Food UK. Retrieved August 13, 2018.
- Gledhill, David (2008). The Names of Plants (PDF) (4th ed.). Cambridge University Press. p. 250. ISBN 9780521866453. Archived from the original (PDF) on January 7, 2020. Retrieved October 18, 2018.
- MacDonald, Francine; Anderson, Hayley (May 2012). "Giant Hogweed (Heracleum mantegazzianum): Best Management Practices in Ontario" (PDF). Ontario Invasive Plant Council, Peterborough, ON. Retrieved September 1, 2018.
- 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, John A. N.; Curtis, T. (2011). Webb's An Irish Flora (8th ed.). 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 February 23, 2007.
- "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)". plants.usda.gov.
- "Giant hogweed: Not widely spread in Michigan". Landscaping.
- Diebel, Matthew (June 18, 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.
- "Be aware of Giant hogweed and avoid contact". www.nidirect.gov.uk. NIDirect Government Services. Retrieved October 22, 2020.
- "Invasive weeds". www.coventry.gov.uk. Coventry City Council. Retrieved October 22, 2020.
- "Giant hogweed (Hereacleum mantegazzianum)". www.gov.im. Isle of Man Government. Retrieved October 22, 2020.
- "How to spot giant hogweed | CTV News". www.ctvnews.ca. July 15, 2010. Retrieved December 8, 2018.
- "Giant Alien". Giant Alien Project, project no. EVK2-CT-2001-00128, European Union. Archived from the original on October 3, 2016.
- "Giant alien — Result In Brief". Retrieved July 4, 2018.
- "Giant Hogweed (Heracleum mantegazzianum) – A pernicious invasive weed: Developing a sustainable strategy for alien invasive plant management in Europe". Retrieved July 4, 2018.
- "List of Invasive Alien Species of Union concern". Retrieved July 4, 2018.
- 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 June 21, 2015.
- "The Return of the Giant Hogweed". Musixmatch. Stratsong Ltd., Quartet Music Ltd., Stratsong Limited.
- "What happened on The Walking Dead this week?". NME. October 21, 2019.
- "The Curse of the Giant Hogweed by Charlotte MacLeod".
- Data related to Heracleum mantegazzianum at Wikispecies
- Media related to Heracleum mantegazzianum at Wikimedia Commons
- Giant Hogweed (Heracleum mantegazzianum): A Federal Noxious Weed U.S. Department of Agriculture
- "Giant Hogweed". the Ontario [Canada] Federation of Anglers & Hunters.
- 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.
- Species Profile – Giant Hogweed (Heracleum mantegazzianum), National Invasive Species Information Center, United States National Agricultural Library.
- Antonova, Maria, "A Toxic Alien Is Taking Over Russia," The New York Times, October 3, 2020
- The Day of the Giant Hogweed! John Harrison