Heracleum sosnowskyi

Heracleum sosnowskyi, or Sosnowsky's hogweed, is a monocarpic perennial herbaceous flowering plant in the carrot family Apiaceae. Its native range includes the central and eastern Caucasus regions of Eurasia and extends into the southern Caucasus region called Transcaucasia. The native ranges of Heracleum sosnowskyi and H. mantegazzianum, a close relative, overlap in the Caucasus region. Sosnowsky's hogweed is now a common weed in the Baltic States, Belarus, Great Britain, Poland, Russia, and Ukraine.

Description
Heracleum sosnowskyi is 3-5 m in height, with a straight, firm stem that can reach a diameter of 12 cm. The leaves are 50-60 cm long. The root is very firm, up to 30 cm diameter. The inflorescence is a big umbel found at the end of every stem. It blooms from July to September and produces thousands of seeds, which are easily distributed by wind, but especially by water.

As Sosnowsky's hogweed is a monocarpic perennial species, the entire plant (including the root) dies after flowering and producing seed.

Similar species
Similar tall invasive species include H. mantegazzianum and H. persicum. Similar noninvasive species include H. sphondylium and H. maximum.

Additionally, wild parsnip, garden angelica and wild angelica may be similar.

Taxonomy
Early botanists considered H. sosnowskyi to be a subspecies of H. mantegazzianum. Sosnowski's hogweed was described as a separate species by Ida P. Mandenova in 1944. The species is named in honor of the Russian botanist Dmitrii Ivanovich Sosnowsky (1885–1952), who found the species in Georgia in 1936.

Invasiveness
In the European Union, Sosnowsky's hogweed is included since 2016 in the list of Invasive Alien Species of Union concern (the Union list). This implies that this species cannot be imported, cultivated, transported, commercialized, planted, or intentionally released into the environment in the whole of the EU.

Control measures
The plant was common only in the Caucasus area until it started to be used as a silage plant in other parts of the Soviet Union. As a result, it quickly spread in many areas of Russia, Belarus, and Ukraine. It is now a highly invasive plant in the Baltic States, Russia, Poland, and Belarus. Many river valleys and roadsides host large stands of this weed. It is difficult to eradicate because the seeds remain viable for many years and the roots are difficult to remove. Herbicides are widely used in a fight against it, but the plant can later resprout from the roots.

The plant is also used as a shield-hedge along the roads, preventing farm animals from escaping and wild animals from getting in.

The decision to use the plant for silage was made in 1947 under Stalin's rule, so when the species later proved to be highly invasive and difficult to remove, people started to call it "Stalin's revenge".

In February 2024, several lawmakers in the State Duma of Russia introduced a so-called "anti-hogweed bill" that would require property owners to remove the plant from their properties and impose a 50,000 ruble ($540) fine for individuals and 700,000 rubles ($7,550) for legal entities who fail to do so.

Phototoxicity


All parts of H. sosnowskyi contain phototoxic furanocoumarins. It is dangerous for humans because even small drops of the plant's juice cause skin photosensitivity and burns. The plant is less dangerous for animals that have thick hair to protect them from the sun.