|Heracleum mantegazzianum Sommier et Levier
|The giant hogweed belongs to the Apiaceae (or Umbelliferae) family, which has more than 2,500 species in 275 genera. These include common herbs like cow parsnip (sometimes called hogweed), anise, carrot, celery, coriander, dill, fennel, parsley, and parsnip, as well as the highly toxic hemlocks
|Native to Asia, more specifically the Western Caucasus, but is now extended in Europe and North America. In the United States, this species escaped cultivation and has become a public health hazard, found in urban, suburban, and rural settings. The giant hogweed is generally found in sunny, humid, and disturbed habitats. It is a serious weed that invades areas that are likely to be highly used by people, such as river and stream banks, roadsides, and rights-of-way.
|It is a giant perennial herb ranging in height from 2.0 to 5.0 m, which can live for several years. It has a large dark reddish purple stem (c. 10 cm in diameter) and speckled leaf stems, both hollow. The compound leaves of H. mantegazzianum can expand to more than a meter in width, deeply incising each leaflet. The inflorescences are composed of many small white flowers and are arranged in large umbels that can grow up to 1.0 m in diameter.
|It is a popular plant in gardens due to its attractiveness.
|The sap of H. mantegazzianum contains psoralens (furocoumarins) that lead to phytophotodermatitis, which is produced by the interaction of these plant compounds with sunlight on human skin. Psoralens are lipid-soluble and penetrate the epidermis easily. The photochemical excitation of psoralens is induced by Ultraviolet radiation, generally within the UVA wavelengths of 320-400 nm. Note that the absorption of psoralens into the skin (and the consequent reaction) is enhanced by humidity.
Two types of toxic reactions occur: one independent of oxygen where ultraviolet activated psoralens bind RNA and nuclear DNAand an oxygendependent reaction where induced compounds cause damage to the cell membrane and edema. These reactions consequently lead to cell death.
Phytophotodermatitis is a phototoxic reaction, and not allergic, so there is no immune reply. As a result, no prior sensitization is necessary and anyone can be affected. Heracleum mantegazzianum is one of the leading causes of phytophotodermatitis in the UK and US.
|The giant hogweed is on the US federal noxious weed list, which means that its importation into the country is illegal, as is the interstate and intrastate movement of this species. In New Zealand, H. mantegazzianum is listed in the National Plant Pest Agreement, and is an unwanted product organism under the Biosafety Act of 1993, pursuant to section 2 (1). This prevents their legal sale, spread or distribution within New Zealand
Great care should be taken when removing these plants, and it should be emphasized that contact with dead plant parts and with inanimate objects or pets that have been in contact with such plants is dangerous. The use of waterproof protective clothing and goggles is therefore advisable when dealing with H. mantegazzianum, as is simultaneously avoiding exposure to sunlight.