Giant Hogweed (Heracleum mantegazzianum), or Giant Cow-parsley,
is a member of the family Apiaceae, native to the Caucasus Region and Central
Asia.
As its name indicates, it is characterized by its size and may grow 2-5m
(rarely to 7 m) tall. Except for size, it closely resembles Common Hogweed (Heracleum
sphondylium), Heracleum sosnowskyi or Garden Angelica (Angelica
archangelica).
It is further distinguished by a stout, dark reddish-purple stem and spotted
leaf stalks that are hollow and produce sturdy bristles. Stems vary from 3-8 cm
in diameter, occasionally up to 10 cm. The stem shows a purplish-red
pigmentation with raised nodules. Each purple spot on the stem surrounds a hair,
and there are large, coarse white hairs at the base of the leaf stalk. The plant
has deeply incised compound leaves which grow up to 1-1.7 m in width.
Giant Hogweed is a perennial with tuberous rootstalks which form perennating
buds each year. It flowers from late spring to mid summer, with numerous white
flowers clustered in an umbrella-shaped head that is up to 80 cm (2.5 ft) in
diameter across its flat top.
The plant produces flattened, 1cm long, oval dry seeds that have a broadly
rounded base, and broad marginal ridges.
The Giant Hogweed flowers from late spring to mid summer, and then produces
numerous, large flattened elliptic dry seeds (between 1,500-100,000). Shoots die
down in the fall. Tall stems mark its locations during winter.
Many foreign plants were introduced to Britain in the 19th century, mainly
for ornamental reasons. A few have become aggressively dominant, creating
serious problems in some areas. It is now widespread throughout the British
Isles especially along riverbanks. By forming dense strands they can displace
native plants and reduce wildlife interests. It has also spread in the
northeastern and northwestern United States. It is equally a pernicious invasive
species in Germany, France and Belgium, overtaking the local species. It was
introduced in France in the 19th century by botanists, much appreciated by
beekeepers.
In the UK the Wildlife and Countryside Act 1982 makes it an offence to plant
or cause Giant Hogweed to grow in the wild.
Toxic
Giant Hogweed is a phototoxic plant. Its sap can cause photodermatitis, skin
inflammations when the skin is exposed to sunlight or to UV-rays. Initially the
skin colours red and starts itching. Then blisters form as in burns within 48
hours. They form black or purplish scars, which can last several years.
Hospitalisation may become necessary. Presence of minute amounts of sap in the
eyes, can lead to temporary or even permanent blindness. These reactions are
caused by the presence of linear derivatives of furocoumarin in its leaves,
roots, stems, flowers, and seeds. These chemicals can get into the nucleus of
the epithelial cells, forming a bond with the DNA, causing the cells to die. The
brown colour is caused by the production of melanin by furocoumarins. In
Germany, where this plant has become a real nuisance, there were about 16,000
victims in 2003.
Keep children away from this plant. Wear protective clothing when handling it
if you dig plants; consider wearing eye protection. Chopping out the root is
feasible, but may have to be done several times as the plant re-grows. Wash off
exposed skin thoroughly with soap and water and protect the exposed skin from
the sun for several days.
Keep the plant mowed down during the summer to prevent seeds from maturing.
Don't allow pieces of it to land on bare skin. Even after the parent plant is
completely removed, the numerous seeds left behind can come up, 7 to 15 years
later. Ongoing monitoring is required. Removing the green growth will help to
exhaust the root and will weaken the plant, so digging it out (as far as 60 cm
deep) and chopping it is feasible.
2,4-D, TBA, MCPA and dicamba will kill above ground parts but are reportedly
not particularly effective on persistent rootstalks. Glyphosate (Roundup) is
considered the most effective herbicide and should be used cautiously around
desirable species since it is nonselective. Application during bud stage and
while the plant is actively growing is recommended by New York Cooperative
Extension.
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Source. |
Close up view of
Hogweed
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Musical reference
"Return of the Giant Hogweed" by Genesis, on the album Nursery Cryme
(1971) tells the story of "regal hogweed" being brought from Russia by a
Victorian explorer to the Royal Gardens at Kew and how it was spread throughout
England by "fashionable country gentlemen". The hogweed then "prepares for an
onslaught, threatening the human race" and people must run for shelter and
attack it at night, as it cannot photosensitize its venom.
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