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      Heracleum mantegazzianum seeds (Photo: USDA APHIS PPQ, - Click for full size   Heracleum mantegazzianum plant (Photo: Donna R. Ellis, University of Connecticut, - Click for full size   Heracleum mantegazzianum (Photo: Terry English, USDA APHIS PPQ, - Click for full size   A burn caused by Heracleum mantegazzianum (Photo: USDA APHIS, - Click for full size   Heracleum mantegazzianum (Photo: Randy Westbrooks, U.S. Geological Survey, - Click for full size   Heracleum mantegazzianum flowers (Photo: Terry English, USDA APHIS PPQ, - Click for full size   Heracleum mantegazzianum foliage (Photo: Donna R. Ellis, University of Connecticut, - Click for full size
    Taxonomic name: Heracleum mantegazzianum (Sommier & Levier)
    Synonyms: Heracleum asperum M. Bieb., Heracleum giganteum Fischer ex Hornem., Heracleum lehmannianum Bunge, Heracleum persicum Desf. Ex Fischer, Heracleum sibricum Sphalm , Heracleum stevenii Manden, Heracleum villosum Fischer ex Sprengel
    Common names: barszcz mantegazyjski (Polish), barszcz mantegazziego, berce de caucase, berce de Mantegazzi (French), berce du caucase (French), bjarnarkló, cartwheel flower (English), giant cow parsnip (English), giant cow persicum (English), giant hogweed (English), Herkulesstaude (German), hiid-karuputk, jättebjörnloka, jättefloka, kæmpe-bjørneklo (Danish), kæmpe-bjørneklo, kaukasianjattiputki (Finnish), Kaukasischer Barenklau (German), kaukasisk jattefloka (Swedish), kaukasisk jättefloka, kjempebjonnkjeks (Norwegian), mantegaci latvanis, mantegaco barštis, Riesenbarenklau (German), tröllahvönn, wild rhubarb (English)
    Organism type: herb
    Heracleum mantegazzianum is native to Asia and has been introduced into Europe and North America. It is characterised by its size and may grow to 4.5 to 6 metres in height. It is most common along roadsides, vacant lots, streams and rivers, and can be considered an invasive freshwater weed. It forms a dense canopy, out-competing native riparian species and results in an increase in soil erosion along the stream banks where it occurs. Heracleum mantegazzianum germinates from early spring throughout the growing season, after exposure to winter temperatures. H. mantegazzianum exudes a clear watery sap that sensitises the skin to ultraviolet radiation which can result in severe burns. Populations in urban and suburban areas represent an increasing public health hazard. Glyphosate is considered the most effective herbicide.
    Heracleum mantegazzianum, or giant hogweed, is a perennial, monocarpic herb in the carrot and parsley family, Apiaceae (Krinke, et al, 2005). It is very tall, typically growing to 3-4 meters in height and may exceed 5 meters (Page et al, 2006). Its inflorescences are white, sometimes pinkish, compound umbels up to 80 cm across with 30-150 rays (Neilson et al, 2005; EPPO, 2006). Individual flowers are on pedicels 10-20 mm long and have petals up 12 mm long (EPPO, 2006). Terminal umbels are the largest and are surrounded by satellite umbels and additional umbels may occur on auxiliary stems (Krinke et al, 2005). Stems are rigid, stout, and typically 5-10 cm in diameter. Stems and leaf stalks are either completely or spotted dark reddish-purple in color, hollow, and produce postulate bristles that produce phototoxic sap (Neilson et al, 2005; EPPO, 2006). H. mantegazzianum has a thick, yellow branching taproot 15 cm in diameter and up to 60 cm long (Page et al, 2006; EPPO, 2006). Leaves are alternate with lower leaves 1-2.5 meters long, compound, irregularly shaped in ternate or pinnate segments, deeply lobed, and irregularly toothed. Upper leaves are smaller and sometimes not divided with longer petioles and more inflated sheaths. Leaves are usually pubescent on the underside when young and glabrous above (Page et al, 2006). Fruits are dry schizocarps consisting of two mericarp seeds 6-18 mm long, 4-10 mm wide and about 1 mm thick, which are joined until ripening. Mericarps are elliptical, flattened, and emarginate at the apex with thin low dorsal ridges and broadly winged lateral ridges (Page et al, 2006; Tiley et al, 1996). The endosperm is oily and mature fruits have a strong resinous smell (Tiley et al, 1996).
    Similar Species
    Heracleum lanatum, Heracleum maximum

    Occurs in:
    agricultural areas, natural forests, planted forests, range/grasslands, riparian zones, ruderal/disturbed, scrub/shrublands, urban areas
    Habitat description
    In its native range, Heracleum mantegazzianum is found on forest edges and glades, in riparian zones, and in mountainous areas with annual rainfall of 1000-2000 mm and a temperate continental climate of hot summers and cold winters. In nonnative locations, giant hogweed is typically introduced to ornamental gardens and spreads along river courses, roadsides, railways, vacant lots and other disturbed locations to invade sunny, moist locations (EPPO, 2006; EIAS, 2003; Pysek & Prach, 1993; Pysek & Pysek, 1995; Tiley et al, 1996; Washington State Department of Ecology, undated). Cold winters are required to ensure germination, but may also be necessary for flowering. It is most associated with temperate deciduous forest and mixed conifer forest vegetation zones (EPPO, 2006). Although it is generally a plant of open ground, H. mantegazzianum can establish and grow successfully in edges of clearings and partially shaded habitats, preferring moist conditions for much of the year, but can tolerate moderate summer droughts (Tiley et al, 1996). It is usually found on alkaline or only slightly acidic soils, from pH 6.0 to 8.5, and appears to be favored by soils with high nitrogen content. Occurrence of giant hogweed along riverbanks is usually associated with sandy or silty soils, but it is also recorded on a wide range of soil textures from gravels to clay and highly organic or waterlogged soils are also tolerated. (EPPO, 2006).
    General impacts
    Heracleum mantegazzianum is considered to be one of the most problematic invasive plants in Europe (Pysek et al, 1998). It produces a toxic sap that causes a painful and problematic phototoxic reaction. It establishes dense monocultures that threaten natural ecosystems. It is also known to increase erosion of river and stream banks and to be a problematic weed in both agricultural and urban environments.

    The sap of H. mantegazzianum causes a phytotoxic reaction when in contact with the skin and exposed to sunlight (Klingenstein, 2007). Toxic furanocoumarins or psoralens are stored as biologically active aglycones in sap in the oil channels or ducts in the leaves, stems, roots, flowers and seeds. When they come in contact with the skin they cause an extreme sensitivity to sunlight called phytophotodermatitis (CEH, 2004). The phototoxic reaction is can be activated by ultraviolet radiation only 15 minutes after contact, with a sensitivity peak between 30 min and two hours (Klingenstein, 2007). It can lead to severe slow healing burns or scarring (EIAS, 2003). Blistering occur s 24-48 hours after exposure to sunlight and dense post inflammatory hyper-pigmentation is visible after 3-5 days and may persist for up to 6 years (CEH, 2004; Klingenstein, 2007). Gardeners, landscape workers, and children are at particular risk. Since the plant itself is painless workers or children in contact with the plant may continue exposure to the sap for hours (Klingenstein, 2007). Its hazard to human health causes H. mantegazzianum to lower the recreational value of invaded lands (Pergl & Perglova, 2006).

    Giant hogweed changes species composition and reduces species diversity of native plant communities (Neilson et al, 2005). It establishes dense stands that displace and suppress the growth of native flora, especially in disturbed areas and riparian zones (CEH, 2004; Neilson et al, 2005; Page, 2006). H. mantegazzianum outcompetes native plants by shading them out, growing leaves above resident herbs and grasses (Thiele & Otte, 2007). It may also have allelopathic properties (Page, 2006).

    Its replacement of native vegetation results in other effects to ecosystems and likely causes far reaching impacts. It displaces native riparian vegetation and then causes bank erosion in the winter it dies back (Page, 2000). Such instability of river banks caused by giant hogweed poses a serious threat to salmon spawning habits in Ireland (Caffrey, 1999). H. mantegazzianum is also known to hybridize with European native Heracleum sphondylium (Klingenstein, 2007), and be a problematic weed to agricultural and urban environments (Page , 2006).

    Heracleum mantegazzianum is a very popular ornamental. Many introductions to new locations are the result of its planting in ornamental gardens or growth for use in flower arranging. H. mantegazzianum is reportedly widely planted in Switzerland by beekeepers to increase food resources for bees. The dried fruits of the plant are used as a spice in Iranian cooking (Westbrooks, 1991). H. mantegazzianum has been cultivated for silage in Russia and has been suggested as a forage crop in Poland (EPPO, 2006).
    The sap of Heracleum mantegazzianum causes a skin reaction that sensitizes skin to sunlight that results in severe swelling in blisters. Contact of skin to the plant should be avoided (Westbrooks, 1991).
    Geographical range
    Native range: The western Caucasus Mountains of Georgia, Azerbaijan, and southern Russian Federation
    Known introduced range: Austria, Australia, Belgium, Canada, Czech Republic, Denmark, Estonia, Finland, France, Germany, Hungary, Iceland, Ireland, Italy, Latvia, Netherlands, New Zealand, Norway, Poland, Slovakia, Sweden, Switzerland, United Kingdom (UK), United States (USA)
    Introduction pathways to new locations
    For ornamental purposes: H. mantegazzianum has been introduced to Europe, the United Kingdom, Canada and the United States as a garden curiosity (The Washington State Department of Ecology (UNDATED)).

    Local dispersal methods
    Consumption/excretion: One way H. mantegazzianum may be spread is by consumption of the fruits or mericarps by birds (Anonymous, 1981b, in Westbrooks, 1991).
    For ornamental purposes (local): H. mantegazzianum has been introduced to Europe, the United Kingdom, Canada and the United States as a garden curiosity (The Washington State Department of Ecology (UNDATED)).
    Hikers' clothes/boots: Because of their propensity to grow in disturbed habitats transfer of soil from human frequented areas is also a common means of dispersal (Gelpke, 2000).
    Other (local): Bee-keepers have played a significant role in spreading the plant, as it is the prefered food for honeybees (Gelpke, 2000).
    Water currents: Seeds of H. mantegazzianum can be spread by water currents (Gelpke, 2000).
    Heracleum mantegazzianum is an amphimictic perennial whose flowers are insect pollinated and self compatible (EPPO, 2006). It is also monocarpic and only reproduces once, usually in its third or fourth year (Pergl & Perglova, 2006; Page et al, 2006). Reproduction is done only by seeds which are copiously produced, from 5,000-100,000 per plant (EPPO, 2006). Seeds remain viable for up to 7 years and possibly longer (CEH, 2004). Flowering typically lasts from June to August. Flowers are compound umbels with 30-150 rays per flower and a total of more than 80,000 flowers can occur on a single plant (Klingenstein, 2007). Fruits are broadly winged schizocarps composed of two mericarps 6-18 mm long and 4-10 mm wide (Krinke et al, 2005; Tiley et al, 1996).
    Lifecycle stages
    The seeds of giant hogweed germinate from early spring and continue throughout the growing season. Cold winter temperatures are necessary to break dormancy (EPPO, 2006). Seedlings initiate a vegetative rosette pattern of growth for the first season that may last 3-4 years (PBPI, undated; Pergl & Perglova, 2006). This phase allows rapid growth and dense development to outgrow and shade out competitive vegetation. H. mantegazzianum may postpone flowering until conditions are favorable and sufficient reserves are stored. When it does flower it flowers early and in great abundance (Neilson et al, 2005). Seedlings reach high densities of several thousand/m2 (Klingenstein 2007), and seed banks reach densities of up to 12,000/m2 (Neilson et al, 2005). On average only 10% of plants flower each year while remainders survive in the rosette stage to the next year (Klingenstein, 2007). In winter foliage dies back and re-grows from the stem and taproot in the spring (Pysek, 1991; PBPI, undated).
    Reviewed by: Anon
    Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Wednesday, 23 February 2011

ISSG Landcare Research NBII IUCN University of Auckland