Cow parsnip (Heracleum maximum) (Heracleum mantegazzianum)

Introduction:

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.

Description:

Heracleum mantegazzianum, or giant hogweed, is a perennial, monocarpic herb in the carrot and parsley family, Apiaceae. 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. Individual flowers are on pedicels 10-20 mm long and have petals up 12 mm long. Terminal umbels are the largest and are surrounded by satellite umbels and additional umbels may occur on auxiliary stems. 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. H. mantegazzianum has a thick, yellow branching taproot 15 cm in diameter and up to 60 cm long. 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. 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. The endosperm is oily and mature fruits have a strong resinous smell.

Occurs in:

Agricultural areas, natural forests, planted forests, range/grasslands, riparian zones, ruderal/disturbed, scrub/shrublands, urban areas.

Distribution Map:

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 location. 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. 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. 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.

General impacts:

Heracleum mantegazzianum is considered to be one of the most problematic invasive plants in Europe. 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. 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. 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. It can lead to severe slow healing burns or scarring. 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. 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. Its hazard to human health causes H. mantegazzianum to lower the recreational value of invaded lands

Sorced From: http://www.issg.org/database/species/ecology.asp?fr=1&si=418