Giant Hogweed
Latin name
Heracleum mantegazzianum
Family
Apiaceae
Flowerlng season
June to August
English distribution
It is found throughout the country.
See the BSBI distribution map for Giant Hogweed
Habitat
It is a neophyte which was planted in gardens and estates
in the 1820s and has continued to escape ever since.
It can form large colonies in wasteland, tips and derelict
gardens and along streams and rivers.
Description
Giant Hogweed is a huge, truly spectacular herb, growing
up to 5m.
Flowers are white and in umbels up to 1m across.
They are 5-merous and the outer flowers of the secondary
umbels have petals that are notched and unequal.
Stems are hollow, hairy and with red patches.
The cross section of the stem in winter (picture 8) can be
up to 10cm.
The leaves are up to 1m across and lime green.
A poisonous plant
Giant Hogweed causes skin irritation (dermatitis) and
is classed as a poisonous plant. It became famous in
the 1970s when it became known as the Triffid from
Behind the Iron Curtain.
Children developed blisters from using stems as blow-
pipes and telescopes, and workmen clearing Giant
Hogweed stands were also affected.
The burns, blisters and rashes are caused by
furocoumarins in the bristles and sap which react with
sunlight to cause photodermatitis.
The same toxins are found in Hogweed and Wild Parsnip,
but in lower concentrations.
How often does it happen?
In June and July 2015 there was a lot of publicity about
the danger of exposure to Giant Hogweed with some
unpleasant pictures of its effects in the media, so clearly
it is still causing problems.
However, West Dorset is a hotspot for Giant Hogweed,
with extensive stands on the Rivers Brit and the Char,
but my local Doctor has never seen a case.
Legislation
Because Giant Hogweed causes skin irritation it is classed
as a poisonous plant. It is listed under Schedule 9 to the
Wildlife and Countryside Act 1981 with respect to England,
Wales andScotland. As such it is an offence to plant of
otherwise cause Giant Hogweed to grow in the wild.
Under the Environmental Protection Act 1990, Giant Hogweed
is classified as controlled waste. For details of legislation
go to www.nonnativespecies.org/legislation.
Control and management of invasive alien (non-native)
plants is under the auspices of a Defra committee - NSSS
(GB Non-native Species Secretariat).
For details for Giant Hogweed, click on the link.
Although it is on the list of controlled plants, it appears to
be on the increase.
Previous page: Garden Lobelia
Next page: Giant-rhubarb
Giant Hogweed, river Brit, Dorset
Giant Hogweed - KJ (5'11") - for size
Umbels can reach 1m across
Newly opened secondary umbel
Outer flower with different sized petals
Giant Hogweed seeds
Large leaves (up to 1m across)
Red spotted stem
Hollow stem in winter (10cm across)
Opening flower bud - 15" across