Giant Hogweed
Species and Names
Species/ Heracleum mantegazzianum
Common Names/ Cartwheel flower, giant cow-parsnip
| Height | Can reach 5m – Tallest UK herbaceous plant |
| Stem | Red spotted, roughly hairy, thick (upto 100mm), robust, hollow, ridged, with hairs |
| Leaves | To 1m long, once-pinnate, deeply lobed, sharp toothed, rough, leaflets to 150mm long with stalks, leaf stem clasping the main stem |
| Flower | Umbels to 500mm across, stalked, petals to 12mm long, whitish green, notched |
| Seeds | To 10mm long winged |
Giant hogweed is one of the most invasive plant species found in the United Kingdom. It spreads very quickly and dominates native plants. Its sap can cause severe chemical burns if it comes in contact with a person’s skin.
Why is it in the UK?
Similar to Japanese knotweed, giant hogweed was introduced in the 19th century as an ornamental plant.
How does it spread?
It spreads through seed dispersal. Each umbrella-shaped flower head can produce in the region of 1500 seeds. Giant hogweed is prevalent along riverbanks throughout the United Kingdom due to its seeds being distributed by the waterways. Strong winds can cause the seeds to travel over great distances. Evidence of this can be found beside many large roads across the country.
What damage can it cause?
Giant hogweed is a phototoxic plant which means the sap of this plant becomes toxic when exposed to UV rays. If the sap comes in contact with human skin it can cause inflammation and blistering if exposed to sunlight or UV rays. This is known as phytophotodermatitis and can leave skin badly scarred.
In addition to these health risks, Giant hogweed can also have damaging effects on ecosystems. As with all invasive plants it is an aggressive competitor which can dominate habitats making them inhabitable to other species and reducing species diversity. Reducing species diversity lowers the ecological value of a habitat. Giant hogweed is a non-native species which can thrive in this country giving it a competitive edge on native species, in particular plants with restricted distribution and habitat requirements.
Often Mistaken for...
Other members of the carrot family such as Wild Carrot (Daucus carota), Hogweed (Heracleum sphondylium), and Angelica (Angelica sylvestris).
