| Heracleum mantegazzianum | |
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| Heracleum mantegazzianum, native, Zelenchuksky District, Karachay-Cherkessia, Caucasus Mts, Russia | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Asterids |
| Order: | Apiales |
| Family: | Apiaceae |
| Genus: | Heracleum |
| Species: | H. mantegazzianum |
| Binomial name | |
| Heracleum mantegazzianum | |
Heracleum mantegazzianum, commonly known asgiant hogweed,[2][3][4][5] is amonocarpic perennialherbaceous plant in the carrot familyApiaceae.H. mantegazzianum is also known ascartwheel-flower,[3][4][5]giant cow parsley,[6]giant cow parsnip,[7] orhogsbane. In New Zealand, it is also sometimes calledwild parsnip (not to be confused withPastinaca sativa) orwild rhubarb.[4]
Giant hogweed is native to the westernCaucasus region of Eurasia. Introduced to Britain as anornamental plant in the 19th century, it has also spread to other areas of Western Europe, as well as the United States, and Canada.[2] Its close relatives,Sosnowsky's hogweed andPersian hogweed, have similarly spread to other parts of Europe.
The sap of giant hogweed isphototoxic and causesphytophotodermatitis in humans, resulting in blisters and scarring. These reactions are caused byfuranocoumarin derivatives found in the leaves, roots, stems, flowers, and seeds of the plant. Consequently, many regions consider it anoxious weed.[2]
The genus nameHeracleum is fromLatin:Hēraclēus, the Latin rendering ofAncient Greek:Ἡράκλειος :Hērákleios 'Hercules', in reference to the giant nature of hogweeds.
The species namemantegazzianum refers toPaolo Mantegazza (1831–1910), Italian traveller and anthropologist.[8]
Giant hogweed typically grows to heights of 2 to 5 m (6+1⁄2 to16+1⁄2 ft).[2] Under ideal conditions, a plant can reach a height of 5.5 m (18 ft).[9][10] The leaves are incised and deeply lobed. A mature plant has very large leaves,1–1.5 m (3+1⁄2–5 ft) wide,[11] sometimes even up to 2.6 m (8.5 ft) wide and up to 3 m (9.8 ft) long[12] and a stout, bright greenstem with extensive dark reddish-purple splotches and prominent coarse white hairs, especially at the base of theleaf stalk. The hollow, ridged stems are 3–8 cm (1–3 in) in diameter, occasionally reaching 12.5 centimetres (5 in) diameter,[13] and can grow to more than 4 m (13 ft) high. Dark red spots on the stem each surround a single hair.[14] The umbrella-shaped inflorescence, known as a compoundumbel, can reach a diameter of up to100 cm (3+1⁄2 ft) across its flat top. The flowers are white or greenish white and may be radially symmetrical or strongly bilaterally symmetrical (zygomorphic).[10] The fruit is aschizocarp, producing dry, flattened, oval seeds in pairs.[10] The seeds are approximately1 cm (1⁄2 in) long, with a broadly rounded base and broad marginal ridges. They are coloured tan with brown lines (so-called oil tubes) running3⁄4 of the seed's length.
The life cycle of giant hogweed consists of four phases:[15]
Emerging seedlings tend to be morphologically diverse, with jagged pinnate forms and more rounded leaf shapes being sighted almost always occurring within the same seed bank.[16] During the first few years of growth, the leaves and stem of a pre-flowering plant die back over winter. In spring, the plant grows back from its root. In other words, the giant hogweed is aherbaceous perennial.
A giant hogweed plant usually produces a flowering stalk in 3–5 years,[2][17] but plants may take up to eight years to flower if conditions are unfavourable. In the Czech Republic, a single plant reached twelve years old before flowering.[18] In any case, when the plant finally flowers, it does so between June and July (in the northern hemisphere).
Seeds are typically produced in August. On average, a single flowering plant will produce 20,000 seeds[19][17] with seed production varying between 10,000 and 50,000 seeds per plant.[18]
Giant hogweed is amonocarpicperennial.[17][9][10] This means that after a mature plant flowers and produces seeds, the entire plant dies. During the following winter, the tall dead stems mark the locations where the flowering plants once stood.
The seeds are dispersed over short distances by the wind, but they can also be carried over longer distances by water, animals, and people. Most seeds (95%) are found within the top 5 cm (2 in) of soil, a few metres of the parent plant. Seeds may remain viable in the seedbank for over five years.[18][19]
A seed deposited in the seed bank is initially dormant. Dormancy is broken by the cold, wet conditions of autumn and winter. Therefore, freshly deposited seeds remain dormant until at least the following spring, when approximately 90% of them will germinate.[17][9] 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 of the seeds produced by self-pollination will germinate and give rise to healthy seedlings,[17] so a single isolated seed can lead to the formation of a new colony of plants.
The various species of the genusHeracleum are similar in appearance, but vary in size.[9]H. mantegazzianum is among the tallest, typically reaching 4 m (13 ft) high (and sometimes more than 5 m or 16 ft high), whereasHeracleum species native to western Europe, such asH. sphondylium ([common] hogweed), or North America, such asH. maximum (cow parsnip), rarely exceed 3 m (10 ft) high.[9][11][17] There are considerable differences in the size of the umbel, leaves, and stem ofH. mantegazzianum as well.
The following table comparesH. mantegazzianum andH. maximum by feature:
| H. mantegazzianum (giant hogweed) | H. maximum (cow parsnip) | H. sphondylium ([common] hogweed) | |
|---|---|---|---|
| Height | Typically 3 to 4.5 m (10 to 15 ft) tall | Up to 2.5 m (8 ft) tall | Up to2 m (6+1⁄2 ft) tall, rarely 2.5 m |
| Leaves | Compound, lobed leaves typically100 cm (3+1⁄2 ft) wide, up to 150 cm (5 ft) wide; mature leaf has deep incisions and serrated edges | Compound, lobed leaves up to 60 cm (2 ft); mature leaf is less incised with less jagged edges | Compound, lobed leaves up to 60 cm (2 ft); mature leaf is with rounded, less jagged edges, hairy |
| Stem | Green stems from 3–8 cm (1–3 in) in diameter, occasionally up to 10 cm (4 in) in diameter, withdark 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) | Grey-green ridged stems up to 3 cm (1 in) in diameter, coarsely hairy (no purple splotches) |
| Flowers | White umbel is typically80 cm (2+1⁄2 ft) in diameter, up to100 cm (3+1⁄2 ft) in diameter, with50–150 flower rays per umbel; flowers from mid-June to mid-July | White umbel up to 30 cm (1 ft) in diameter with15–30 flower rays per umbel; flowers from late May to late June | White (occasionally pinkish) umbel up to 25 cm (1 ft) in diameter with12–25 flower rays per umbel; flowers from June to September (sometimes as early as April) |
| Fruit | Narrower oval fruit 9–11 mm long_seeds.jpg) | Heart-shaped fruit_seeds.jpg) | Broad oval fruit 7–10 mm long |
Many more species exist; in Europe alone, there are over 20 species of the genusHeracleum.[17] Few of these reach a similar size, and several arephototoxic to a lesser degree. However, two other species,H. sosnowskyi andH. persicum, do reach similar sizes, and are equally noxious. These three species, alongsideH. lehmannianum andH. asperum, are sometimes grouped into a single species complex.
Giant hogweed is widespread throughout western and northern Europe, especially along terrains such as coastal areas and riverbanks.[2] By forming dense stands, it can displace native plants and reduce wildlife habitats.[2][20] It has spread in the northeastern and northwestern United States and southern Canada, and is aninvasive species across western Europe;[2] in sites where it has settled, it overtakes the local native species,H. sphondylium.[20]
In Canada, the plant occurs in most provinces, exceptin the prairies.[2] It has been present in Quebec since the early 1990s.[21] The plant's spread in Ontario began inthe southwest and it was first observed in theGreater Toronto Area andRenfrew County near Ottawa in 2010.[22]
In the US, giant hogweed occurs in Maine, Wisconsin, and south to Indiana, Michigan, Maryland, and New Jersey.[23][18][24] In June 2018, it was reported growing in Virginia and North Carolina.[25][26] The plant is federally listed as anoxious weed in the US.[23]
The closely related hogweedHeracleum sosnowskyi is widespread in Russia and the Baltic states, and present in eastern Europe.[2]
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Heracleum mantegazzianum is native to the westernCaucasus region ofEurasia.[2] Because of its impressive size, giant hogweed was brought to Europe and North America as an ornamental plant and garden curiosity.
The following historical information[17][27][28][18] grew out of the European Giant Alien Project, which began in 2005.
Heracleum mantegazzianum was first described in scientific literature in 1895, but by that time, the plant had been imported as an 'ornamental curiosity' by more than a dozen European countries. The first recorded introduction ofH. mantegazzianum was first recorded in Great Britain in 1817, when it appeared on the seed list at theKew Botanic Gardens in London. The first natural population was recorded in 1828, growing wild at Shelford inCambridgeshire.[29]
The spread ofH. mantegazzianum throughout Europe continued unabated until the mid-20th century, by which time the dangers posed by giant hogweed had become better known. Despite these warnings, however, the plant continued to be used by gardeners, beekeepers, and farmers (forcattle fodder) for another 50 years.Heracleum mantegazzianum was finally delisted by theRoyal Horticultural Society of Great Britain in 2002.
During the 20th century, giant hogweed was brought to the US and Canada to be displayed in arboretums and Victorian gardens. The earliest recorded instance of its planting in North America was in 1917 in gardens near Highland Park in the city of Rochester, New York.
Giant hogweed first appeared in southern Ontario by 1950, and within a quarter of a century the plant had become firmly established there. The first collections were made in Nova Scotia in 1980 and in Quebec in 1990. Giant hogweed remained on sale in Canadian nurseries until 2005.
On the west coast of North America,H. mantegazzianum appeared in Oregon, Washington, and southwestern Canada, but it is unclear how the species arrived in this region. The first reports of giant hogweed in British Columbia date back to the 1930s.
Heracleum mantegazzianum has not spread in Russia. Another similar very large hogweed species,H. sosnowskyi, also native to the Caucasus region, was introduced into Russian agriculture starting from 1947 as a fodder plant and later spread extensively on its own throughout Russia and some other countries of eastern Europe.[2]
Because of its phototoxicity and invasive nature, giant hogweed is often actively removed. TheEuropean Union funded theGiant Alien project to combat the plant.[30][31][32] On 2 August 2017, it added the species to itsList of Invasive Alien Species of Union concern,[33] 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, theWildlife and Countryside Act 1981 makes it an offence to plant or cause giant hogweed to grow in the wild.[20][34]
In the US, hogweed is regulated as afederal noxious weed, and it is illegal to import it into the US or move it across state borders without a permit from theDepartment of Agriculture (USDA).[35] TheNew York State Department of Environmental Conservation has had an active program to control giant hogweed since 2008.[36] In 2011, Maine state horticulturists reported that it has been found at 21 locations in Maine, with the number of plants ranging from one to a hundred.[37]
Hybrids have been reported between invasive specimens ofH. mantegazzianum and native populations ofH. sphondylium in Britain;[38][39] characteristics of such plants tend to be intermediate between the two species.[40] Hybrids only tend to survive whereH. sphondylium is the maternal plant.[41]
Other specimens have been recorded which have intermediate morphology, but whose hybrid status is uncertain.[42]
The sap of the giant hogweed plant is phototoxic. The sap containsfuranocoumarins, which leads tophytophotodermatitis, a serious skin inflammation.[43] 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.[17][9] Authorities advise that all humans (especially children) should stay away from giant hogweed.[44][45][46] 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.[17][20][43] OtherHeracleum species such asH. maximum, are likewise phototoxic, and hence similar caution is advised. Owing to physical similarities to other hogweeds in the genusHeracleum, giant hogweed and its close relatives are sometimes mistaken for harmless plants.[47]
Poisoning via ingestion by humans is not known to occur, discounting phototoxicity from contact with external tissues, and consumption of small amounts of the plant is not deemed to be harmful.[48] However, it should still be avoided due to the obvious extreme hazards created by proximity to the plant. Consumption by other grazing animals does not appear to cause them harm, andsheep have been trialled as a giant hogweed control agent in Scotland.[49] TheUSDA Forest Service states thatpigs and cattle can eat it without apparent harm.[50]
The 1971 albumNursery Cryme by theprogressive rock groupGenesis contains the song "The Return of the Giant Hogweed". The darkly humorous lyrics[51] describe an attack on the human race by the hogweed, long after the plant was first 'captured' and brought to England by a Victorian explorer.[52]
In her 1985 novelCurse of the Giant Hogweed, popular mystery authorCharlotte MacLeod places her established character Peter Shandy and his colleagues in a fantasy version of Wales to investigate giant hogweed endangering Britain's hedgerows.[53]
The plant is featured inseason 10, episode 3, of the AMC television seriesThe Walking Dead, growing from zombies which a character encounters, rendering him unable to see properly.[54]
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