Heracleum mantegazzianum, commonly known as giant hogweed,[2][3][4][5] is a monocarpic perennial herbaceous plant in the carrot family Apiaceae.

It was introduced to Britain as an ornamental plant in the 19th century, and has also spread to other areas in Western Europe, the United States, and Canada.

A mature plant has huge leaves, 1–1.5 m (3+1⁄2–5 ft) wide,[11] and a stout, bright green stem with extensive dark reddish-purple splotches and prominent coarse white hairs, especially at the base of the leaf stalk.

The life cycle of giant hogweed consists of four phases:[13] During the first few years of growth, the leaves and stem of a pre-flowering plant die over the winter.

[20] The closely related hogweed Heracleum sosnowskyi is widespread in Russia and the Baltic states, and present in eastern Europe.

[2] Because of its impressive size, giant hogweed was brought to Europe and North America as an ornamental plant and garden curiosity.

Heracleum mantegazzianum was first described in scientific literature in 1895, but by that time more than a dozen European countries had already imported the plant as an "ornamental curiosity".

The introduction of H. mantegazzianum was first recorded in Great Britain in 1817 when it was put on the seed list at the Kew Botanic Gardens in London.

[26] The spread of H. mantegazzianum throughout Europe continued unabated until the middle of the 20th century, at which time the dangers of giant hogweed had become more widely known.

The earliest recorded planting in North America was in 1917, in gardens near Highland Park in the city of Rochester, New York.

On the west coast of North America, H. mantegazzianum appeared in Oregon, Washington, and southwestern Canada, but it is not clear how the species found its way into this region.

Another similar very large hogweed species, H. sosnowskyi, also native to the Caucasus region, was introduced into Russian agriculture starting from 1947 as a fodder plant and later spread extensively on its own throughout Russia and some other countries of eastern Europe.

In the United Kingdom, the Wildlife and Countryside Act 1981 makes it an offence to plant or cause giant hogweed to grow in the wild.

[17][31] In the US, hogweed is regulated as a federal noxious weed, and is illegal to import into the US or move interstate without a permit from the Department of Agriculture (USDA).

[34] Hybrids have been reported between invasive specimens of H. mantegazzianum and native populations of H. sphondylium in Britain;[35][36] characteristics of such plants tend to be intermediate between the two species.

Parts of the body that come into contact with the sap of giant hogweed should be immediately washed with soap and cold water, and further exposure to sunlight should be avoided for at least 48 hours.

Consumption by some other grazing animals does not appear to cause them harm, and sheep have been trialled as a giant hogweed control agent in Scotland.

[47] The 1971 album Nursery Cryme by the progressive rock group Genesis contains the song "The Return of the Giant Hogweed".

The darkly humorous lyrics[48] describe an attack on the human race by the hogweed, long after the plant was first 'captured' and brought to England by a Victorian explorer.

[50] The plant is featured in season 10, episode 3, of the AMC television series The Walking Dead, growing from zombies which a character encounters, rendering him unable to see properly.