Giant hogweed is native to the Caucasus Region and Central Asia. It was introduced to Britain as an ornamental in the 19th century, and it has also spread to Ireland, Finland, Sweden, Germany, France, Belgium, Czech Republic, Latvia, the United States and Canada.
The sap of giant hogweed causes phytophotodermatitis in humans, resulting in
blisters, long-lasting scars, and—if it comes in contact with eyes—blindness.
These serious reactions are due to the furocoumarin
derivatives in the leaves, roots, stems, flowers, and seeds of the plant.
Giant hogweed has a stout, dark reddish-purple stem and
spotted leaf stalks
that are hollow and produce sturdy bristles. Stems vary from 3–8 cm
(1.2–3.1 in) in diameter, occasionally up to 10 cm (3.9 in). The
shows a purplish-red pigmentation with raised nodules. Each purple spot on the
stem surrounds a hair, and large, coarse white hairs occur at the base of the
leaf stalk. The plant has deeply incised compound leaves which grow up to
1–1.7 m (3 ft 3 in–5 ft 7 in) in width.
Giant hogweed is a short-lived perennial (lasting typically
between five and seven years), with tuberous rootstalks that form perennating
buds each year. It flowers in its final year from late spring to mid summer, with
numerous white flowers clustered in an umbrella-shaped head that is up to
80 cm (31 in) in diameter across its flat top. The plant produces
1,500 to 100,000 flattened, 1 cm long, oval dry seeds that have a
broadly rounded base and broad marginal ridges. After seeds have set, the
individual plant dies. Plants in earlier stages of growth die down in the
autumn. Tall dead stems may mark its locations during winter.