Giant Hogweed
Scientific Names:
Heracleum mantegazzianum
Other name: Giant Cow Parsnip
Family: Apiaceae
Description and Info:
This spectacular plant (a member of the Umbellifer family) was introduced from the Ural Mountain region by Victorian gardeners. Unfortunately it is now widespread in the wild and causes a number of problems. The stems contain copious amounts of clear watery sap which makes the skin very sensitive to sunlight. On contact the skin can become broken and blistered. It can also cause temporary blindness if it gets into the eye. The leisons appear some hours after contact, heal slowly and can leave the skin permanently sensitised to sunlight - Phytophotodermatitis
It is also a threat to native plants as it colonises riverbanks and other disturbed ground in dense stands blocking out light with its large leaves.
It is a perennial which dies away in the late autumn and comes into growth the following spring. The hollow stems can be 10 cm thick and carry the plant to a height of 3 to 5 metres. They are covered in fine hairs which can cause irritation on contact with the skin. The leaves are compound with 3 leaflets and the lower ones can be up to 1.5 m across on a long, spiny stalk.
The small, white flowers are carried on flat, multi-branched umbels and develop eliptical seed which are 7 to 12 mm long. A single flower head can produce 1500 seed and they can remain viable in the soil for 7 to 8 years.
Under the 1981 Wildlife and Countryside Act/ Wildlife (Northern Ireland) Order 1985, it is an offence in the UK to allow it to grow in the wild. To dispose of any plant material or soil contaminated with it, requires a certificate for Waste Transfer and to be taken to a suitably licensed landfill site.
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Hogweed
Scientific Names:
Heracleum sphondylium
Other name: Cow Parsnip
Family: Umbelliferae
Description and Info:
Hogweed is a biennial, or monocarpic to polycarpic perennial native in grassy places, along hedges, on rough ground, roadsides and banks. It may show a preference for chalk soils. Hogweed is chiefly a problem on pasture but may encroach onto arable land from the hedgerow or headland. However, although common in the hedge bottom it is rarely found further than 2.5 m into the arable field. In a survey of weeds in conventional cereals in central southern England in 1982, hogweed was found in 2, 3 and 1% of winter wheat, winter barley and spring barley fields respectively. It can be a weed of perennial crops such as fruit.
Hogweed flowers from June to September. The flowers are self-compatible and usually insect-pollinated. There are several hundred seeds in each flower umbel. The average seed number per plant in ruderal habitats is 5,030. Seed is shed slowly from August until winter.
Ripe seeds contain a rudimentary embryo that requires 2-3 months at low temperatures to after-ripen. Seed has given 3% germination after 14 days at 5°C and 69% after 96 days. Seeds do not after-ripen fully at higher temperatures and there was no germination of seed kept at room temperature. Seeds buried in soil develop a light requirement for germination.
Seed mixed into the surface soil and stirred periodically emerged from January to June with a peak in March-April. No seedlings appeared outside this period. The majority of seedlings emerged in the first year with only the odd seedling appearing over the following 4 years. Seed sown into short turf in October emerged from March to June with a peak in late-March. Around 50% of the emerged seedlings survived into the summer. In closed communities, seedlings may emerge but not develop further until an opening in the vegetation occurs.
The stems and foliage die down in winter leaving a stout taproot that overwinters.
Based on the seed characters, hogweed seed should persist for less than 5 years and does not form a persistent seedbank.
The seeds are winged and flattened, and may be scattered a short distance by the wind.
