Giant hogweed ( Heracleum mantegazzianum ), in the foreground with a central umbel that has already faded
|Sommier & Levier|
The one or more giant hogweed ( Heracleum mantegazzianum Sommier & Levier , Syn. : Heracleum giganteum . Hornem ), and claws of a bear , giant hogweed or Hercules herb called, is a plant of the family Umbelliferae (Apiaceae). It is a two-year to perennial, if unaffected, once-flowering ( hapaxanthe ) herbaceous plant , so not a perennial . It originally comes from the Caucasus and is an invasive neophyte in Europe and North America .
The giant hogweed forms photosensitizing substances from the group of furocoumarins , which have a phototoxic effect in combination with sunlight or stronger lamp light . Exposure to daylight can cause painful wheals and blisters in humans and other mammals that are difficult to heal and appear like burns ( photodermatitis ). It is therefore recommended to wear full protective clothing , including face protection , when handling the plant .
The giant hogweed was voted poisonous plant of the year in 2008.
In Central Europe, there is a possibility of confusion with the large indigenous umbelliferae, meadow hogweed ( Heracleum sphondylium ) and angelica ( forest angelica , Angelica sylvestris and medicinal angelica , Angelica archangelica ).
Appearance and foliage leaf
The giant hogweed grows as two to perennial-once flowering herbaceous plant , reaching a biennial plant often within a few weeks a stature height up to three meters. The largest plant measured to date, which was entered in the Guinness Book of Records , reached a height of 3.65 meters. The moderately hairy and mostly purple-spotted stem has a diameter of two to ten centimeters at its base. It often has numerous large, dark or wine-red spots.
The leaves usually reach a length of one meter, but can also be three meters long with the petiole. The leaf blade can be pinnately divided into three or five to nine parts . The lateral leaf sections can be more than a meter long and more than 20 centimeters wide and are usually also deeply divided.
Inflorescence, flowers and fruit
The very large central double umbels often reach a diameter of 30 to 50 centimeters. They are 30 to 150 beams. The umbels of a single plant can contain up to 80,000 individual flowers and develop up to 15,000 fruits ( double achenes with two seeds each). The outer flowers are one-sided, enlarged from the center outwards (radiant). Their diameter is 1 to 2 centimeters. The diameter of the flowers inside the umbels, however, is only 4 to 8 millimeters. The flower color is white; the flowering period extends from June to July.
The structure of the flower corresponds to the basic form of all Doldenblütler and with the following floral formula described: .
The achenes are oval, flat, 10 to 14 millimeters long, 6 to 8 millimeters wide and have upwardly curved, bristly hairy marginal ribs and four dark oil welts each. After the achenes form, the plant dies. If it does not flower and the fruit does not ripen, the plant can live for several years. Due to the high number of seeds, the giant hogweed is a plant with a pronounced ability to spread. Your seeds will also remain viable for several years. The maximum duration of the germination capacity can be concluded on the basis of individual experience reports when removing giant hogweed plants. In at least one case, after seven years of grazing by sheep, no new seedlings emerged and the population at the site died out completely.
The number of chromosomes is 2n = 22.
The seeds of the giant hogweed germinate very early in the year; they need a frost effect to break the dormancy. Depending on the microclimate of the respective location, this can happen as early as the beginning to mid-February. Together with the strong growth of the plants, the giant hogweed has a significant advantage over competing plant species. Annual plants reach a height of up to one meter at the beginning of May, when most of the plants native to Central Europe are not yet growing in length. The large leaves shade the remaining vegetation and thus hinder its development. By the end of June, fully grown biennial plants can be more than 3 meters high.
The plant stores starch in a beet-like thickening at the base of the shoot and the upper parts of the root . This enables her to sprout very early in the second year as well as to sprout again after pruning. The giant hogweed can therefore flower despite being mowed several times. If the plant blooms and fruit, this storage reservoir is used up and the plant then dies.
The giant hogweed is one of the nitrogen-loving plants, but otherwise makes little demands on the soil. It just can't cope with very acidic soils. Even if the seed germinates, the seedlings die again within a few weeks in a strongly acidic environment ( pH 3.3 and less). The formation of umbels and thus diaspores only occurs in sunny locations. However, plants in locations with little solar radiation can survive for several years without blooming.
The giant hogweed contains photosensitizing substances as well as essential and fatty oils; the latter, however, are only present in the oil welts of the fruit . The toxic components include the furocoumarins xanthotoxin , psoralen and bergapten . They are contained in all plant components. The white inner lining of the hollow stalks, if present, are poison-free; the stems themselves only when they are completely dead and only the white cell skeleton remains.
The plant originally comes from the Caucasus and is therefore also known as Caucasian hogweed . Its natural range is in the West Caucasus, west of the Elbrus , where it is widespread from the foothills of the mountains to altitudes of 2200 meters, above the tree line. In their homeland, Heracleum mantegazzianum can be found on the edges of forests and clearings, in riparian zones and in mountain regions with an annual rainfall of 1000 to 2000 mm and a temperate continental climate with hot summers and cold winters.
Introduction to Europe
The giant hogweed was first described in 1895 . Numerous earlier mentions of plants in gardens and collections, under the names Heracleum giganteum (among other things mentioned in a seed list of the Kew Gardens from 1817, which is much cited as the first record ), Heracleum pubescens , Heracleum caucasicum and others, are possibly due to other huge hogweed clans of the Caucasus and surrounding regions, the genus Heracleum section Pubescentia , especially Heracleum sosnowskyi , but also Heracleum persicum , so that the early spread remains unclear. However, it is generally believed that the species reached large parts of north-western Europe in the 19th century. The fact that the very eye-catching plant became known so late in Europe has to do with the political history of the area. The West Caucasus, the home of the species, the settlement area of the Circassians , was too risky for explorers for a long time due to the wars of conquest of Russia and its permanent conflict with the Ottoman Empire and only became accessible after the "pacification". After the expedition of the botanists and plant collectors Carlo Pietro Stefano Sommier and Émile Levier in 1887, who described the plant scientifically for the first time, it was quickly spread across Europe as a garden plant.
As an ornamental plant, it is still occasionally used in gardens and parks today.
The central European expansion of the giant hogweed contributed significantly to the fact that the plant was assumed to have an economic benefit. It was repeatedly recommended to beekeepers as a bee pasture in the second half of the 20th century . However, it is mostly dung bees and not honey bees - but not recognizable from below the high cones - that ingest the open nectar. It was used in forestry because with the dense populations of this plant in the summer half-year they wanted to give the game additional cover and were convinced that this plant could be used to fortify embankments. Because of this supposed economic benefit, she was repeatedly anointed in the wild . In Germany, however, this is subject to approval according to the Federal Nature Conservation Act. In Switzerland it was added to the black list of invasive neophytes and subject to the release ordinance.
This Caucasus plant, valued for decades as a particularly decorative plant in its blooming stage, now considered a neophytic pest plant, can now also be found far outside its original natural range. Starting from gardens and parks and, in particular, from locations where it has grown together, it grows on roadsides, in stream and river valleys and on fallow land and can displace native vegetation there. It has decorative fruit stands that are often used as an ornament. The giant hogweed is now widespread throughout Central Europe (central Russia to France, on the British Isles, from Norway to Hungary) and parts of North America and is one of the undesirable neophytes there . Due to its good seeding and its toxic effects, it quickly became a nuisance, because it forms large stocks in a very short time, which are very difficult to remove.
The range of locations where the giant hogweed thrives is much larger than in the area of origin. In Europe, it also spreads to drier and warmer locations than in its homeland and is therefore not only found in the fringing vegetation of hedges , forest edges, streams and rivers, but also on heaps and ruderal sites and even in nature reserves. In Germany it occurs particularly in societies of the Galio-Urticenea subclass.
Spread of wind and swimming
In Europe and North America, the giant hogweed is a human-introduced plant that would not naturally have reached these habitats. It is therefore also known as the hemerochore plant. It uses different propagation strategies both in its new and in its original area of distribution .
The giant hogweed spreads its seeds mainly through the wind ( anemochory ). The spreading distances that are overcome, starting from the mother plant, are up to 180 meters leeward (measured on a hay meadow slope above Freiburg-Littenweiler). The ability of the plant to colonize large areas quickly also results from the floating ability of the seeds for up to three days. Seeds of a plant that stands on the edge of a body of water can cover great distances (swimming spread, nautochory ). Due to flooding, the seeds are also washed up on higher bank areas.
Investigations by invasion biologists have been able to show, using the example of the distribution at the Auschnippe stream north of Dransfeld (Göttingen district), that all giant hogweed colonies along this stream were evidently caused by a single plant in the middle of Dransfeld. From the stream, the giant hogweed successfully conquered other adjacent areas such as meadows or fallow land as well as pastures.
Animal spread and unintended transport
However, the investigations also showed that unintentional transport contributes to the spread of the diaspores (so-called agochory ). Agricultural vehicles in particular are involved. As an example, Kowarik (see references) gives a planting by a beekeeper in the mid-1980s on the Kleiner Drakenberg. Although there were no rivers in this area that encouraged the spread of the giant hogweed, 15 years later there were plants up to 3.5 kilometers away from this original area. This enabled the species to cover an average distance of 233 meters per year. The new occurrences were mainly found along roads that were used by motor vehicles, as well as along game passages , which were mainly passed by wild boars . The latter is cited as evidence that giant hogweed can also zoochor , i.e. be spread by animals.
Giant hogweed as an invasive neophyte
The giant hogweed is classified as an invasive (= penetrating) neophyte and its spread is often perceived very emotionally or sensationally commented on in the press . This reaction is partly due to the fact that the plant harbors significant health risks and even touching it can result in serious health damage.
In addition to the health hazards caused by the giant hogweed, there are also the following:
- In Sweden , the tall giant hogweed perennials on the roadside restricted visibility in traffic .
- Since the roots of the giant hogweed - unlike a closed sward with its root felt that lives on even in winter - do not have an embankment-stabilizing effect, but these plants often thrive on the edge of flowing waters, they can pose an increased risk of erosion during floods . Similar to the deep shade under the colonies of the Japanese knotweed , the grass growth that protects the ground also dies under the large leaves of the giant hogweed, so that the embankment can be removed there.
- There was also a risk of erosion on the slopes of ravines .
- Yield losses can occur when giant hogweed plants grow in fields and meadows.
- Locations dominated by the giant hogweed show a smaller range of species in the herb layer due to the shading. It often spreads to disturbed locations that have already been altered by human intervention, where species on the Red List are rarely found. The giant hogweed also spreads in endangered biotopes such as moist tall herbaceous corridors . In meadows it can also threaten rarer or endangered species such as common meadow silage , meadow cowslip and woolly thistle , or it hinders conservation measures.
The ecological damage caused by the giant hogweed is rather overestimated compared to other invasive neophytes such as the late bird cherry or the common robinia . The broad public perception of the giant hogweed as a problematic neophyte also results from its conspicuousness and from the risks to human health.
Control of the giant hogweed
When it comes to control measures, a distinction is made between large-scale stands and individual plants or small-scale stands. Large numbers of giant hogweed can be combated with herbicides , on suitable areas also by multiple mowing and mulching, milling or by grazing with sheep and goats. The Hercules herb is not eaten by the grazing animals, however, but, similar to the case of Japanese knotweed, only forced, through tight penning. The question of whether a relevant part of the toxins can pass into milk and meat in the feed of livestock, as is the case with the highly poisonous autumn crocus, is still unresolved. The control takes place in the low population at the latest in April, whereby a certificate of competence as well as an exemption from the nature conservation authority may be required when using weed control agents . In the following years, a follow-up check, weeding of emerging seedlings (initially round-leaved!) And possibly mechanical tillage is sufficient.
To control single plants and small stands in early spring and spring, simply cutting them off works immediately, but not necessarily lastingly. It is effective to remove stems with flower umbels before unfolding the central umbel an inch above the ground, i.e. with the main and secondary umbels.
Since the adult plant has reserves for renewed flower formation before the fruits ripen, it often sprouts later and usually also in the following year. If the plant sprouts more dormant buds in the upper part of the root after cutting, only digging or cutting off the root 15 cm below the surface will help. Further young plants can also sprout later in the year, so that regular follow-up checks and, if necessary, control by September is necessary. The young plants with round, whole-edged leaves must also be removed every time in the following years.
Cutting off and disposing of the seed heads in summer shows good success. The seed stand should be cut off when the central umbel has already developed green (heavy) fruits (around mid-July), but before the fruits show the first brown stripes and begin to fall out. The non-seed-bearing sub-umbels are still in full bloom at this time and have to be cut off to dry out on the spot. The seed-bearing umbels ripen and are therefore completely disposed of. The fruit clusters must be removed and must not get into the compost. They are disposed of with the residual waste or incinerated on site.
The mother plant can remain standing and dies before the following winter. Kindels are not educated. The location must be checked in the years thereafter and the clipping repeated every time if necessary. If the certificate of competence is available, systemic herbicides can also be applied to the cut surfaces close to the ground (stem and petiole stumps).
Gloves, protective clothing, protective goggles and, if necessary, respiratory protection are required for removal even on a small scale. As a precautionary measure, a pruning saw or shears with a telescopic handle should be used in high stands to avoid injury from the superficial toxins of the falling plants. Working with overcast skies and only weak winds is recommended. The local nature conservation authority gives advice, takes care of the removal on public areas and in some communities also supports in private gardens. The disposal should be carried out with caution, care and expertise, so that it is ensured that it is giant hogweed and not accidentally other plants, e.g. B. angelica , are destroyed.
Health damage from the giant hogweed
Furocoumarins are contained in and on the entire plant (also in the root system) , which cause phototoxic reactions after skin contact with subsequent exposure to sunlight . For sensitive people, a simple contact with the surface of the leaves is sufficient. The reactions show up in redness, skin inflammation, irritation and in severe cases in blistering dermatitis , which manifests itself in inflammatory and painful blistering. This may be a large area and burns first cause to the second degree. The skin irritations and blisters can cause weeping wounds that last for weeks and are associated with persistent pigment changes . Also fever , sweats and circulatory shock can be the result of contact with the plant.
Under certain circumstances, reactions can also be triggered a few days later by sunlight shining on the affected skin. On hot days, the furanocoumarins are also released from the plant to the environment, and the symptoms described above or even shortness of breath can occur even if the plants stay for a longer period of time . Outgassing furanocoumarins can cause acute bronchitis (lasting up to three weeks) .
When working with the grass trimmer or when chopping off the plant, the sap can also cause effects through clothing.
After contact with parts of the plant, you should avoid the sun and wash the affected areas of skin with soap and water, better with alcohol. A dermatologist should be consulted in the event of skin irritation. Tools used (scythe, spade) should be rubbed from top to bottom with newspaper dipped in alcohol, and the paper should then be burned. Used rubber gloves should be turned inside out and not used again. Thin disposable gloves can be penetrated by the furans within an hour.
The giant hogweed is a relatively young plant in Europe that has only rarely found its way into cultural history. An exception is the song The Return of the Giant Hogweed by the progressive rock band Genesis , which satirically portrays the giant hogweed as a serious danger. It says, among other things, "[...] turn and run, nothing can stop them, around every river and canal their power is growing [...]" ( German : "[...] turn and run, nothing can stop them , on everyone River and canal grow their power […] ”). The piece appeared on the album Nursery Cryme in 1971 . In the nursery rhyme, the good moon goes on its journey by Ute Rink , an idyllic picture is drawn instead: “In the giant hogweed / sits the hedgehog woman / with her hedgehog man - / the two look at each other tenderly.” In the novel Mr. Yamashiro prefers potatoes from Christoph Peters, on the other hand, the protagonist Ernst Liesegang "looked in vain for an article on the giant hogweed" in the latest twenty-five volume edition of Meyer's Encyclopedic Lexicon, which his father had recently acquired, "and there" the speed with which he came out of the swamp behind the house had been growing new leaves and shoots since mid-February, increasingly worried ", he commissioned a retired expert from the Swedish Forestry Administration to remove them. During his active time, he had not succeeded in the increasingly devastating spread of Herculeum giganteum in the past decade and a half Sweden to prevent "and thus decided to" undertake this task v of national, even European importance beyond the day of his retirement. "
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