RiesenBärenklau

Riesen-Bärenklau, known in science as Heracleum mantegazzianum, is a large herbaceous plant in the Apiaceae. Native to the Caucasus, it was introduced to Europe in the 19th century as an ornamental plant and has since spread widely, particularly along riverbanks, roadsides and disturbed sites. It can reach 2–5 meters in height, with enormous, sharply serrated leaves up to 1.5 meters across. The flowers form large white umbels up to 80 cm in diameter.

The plant has a stout stem with purple blotches and coarse hairs. It is a biennial or short-lived perennial; the first year forms a rosette, the second year bolts to produce flowering stems.

Riesen-Bärenklau contains phototoxic furanocoumarins in sap; contact with skin plus UV light can cause severe dermatitis, deep burns and long-lasting scars; accidental exposure near water could cause more intense reaction. Symptoms may appear hours after exposure.

Ecology and control: It spreads by seeds, with plants capable of producing thousands of seeds per season; seeds can remain viable for years. It forms dense stands that displace native vegetation and alter ecosystems. Management includes wearing protective clothing, removing plants before seed set, careful bagging and disposal of plant material, and application of herbicides for larger infestations; multiple, repeated treatments are usually required.

Legal status and safety: In many countries it is listed as an invasive or noxious weed; public agencies advise reporting sightings. Public health guidance includes avoiding contact, washing exposed skin with soap and water, and seeking medical attention for severe reactions.