Heracleum sibiricum

Heracleum sibiricum is a species of flowering plant in the family Apiaceae. It is native to Europe and western Asia, ranging from France and Italy to western Siberia and Mongolia.

Description
Heracleum sibiricum is a herbaceous, perennial, flowering plant with flowers arranged in an umbel. Each flower has five yellowish-green petals. Individual flowers may be bisexual (with a pistil and five stamens), pistillate (with no functional stamens), or staminate (with no functioning pistil). The pistil is bicarpellate and syncarpous, that is, it has two carpels fused together. The ovary is glabrous (hairless) and the stylopodium (at the base of the styles) is almost always green. The fruit is composed of two mericarps, each with a single seed.

Similar species
Heracleum sibiricum is similar in appearance to Heracleum sphondylium, a very close relative. The following table emphasizes the differences between the two species:

The marginal flowers of Heracleum sphondylium are typically zygomorphic (with bilateral symmetry), whereas the marginal flowers of Heracleum sibiricum are actinomorphic (with radial symmetry) or nearly so. Occasionally the marginal flowers of Heracleum sphondylium will be actinomorphic, however.

Both species are variable with respect to the pilosity (hairiness) of the ovary. An atypical form of Heracleum sphondylium may appear to be glabrous to the naked eye but in fact it has short, stiff, ascending hairs with pointy tips. An atypical form of Heracleum sibiricum has similar but even shorter hairs.

Taxonomy
Heracleum sibiricum is one of five species of Heracleum described by the Swedish botanist Carl Linnaeus in 1753 (the other four being H. alpinum, H. austriacum, H. panaces, and H. sphondylium). The specific name sibiricum suggests the taxon occurs in Siberia, a fact mentioned by Linnaeus in his description. In 1887, the Hungarian botanist Lajos Simonkai reduced its taxonomic rank to a subspecies of Heracleum sphondylium. , Plants of the World Online (and a few other authorities) accept Heracleum sibiricum L., but most authorities still recognize Heracleum sphondylium subsp. sibiricum (L.) Simonk.

In 1926, the Swiss botanist Albert Thellung described Heracleum sphondylium var. chaetocarpum, a variety of Heracleum sibiricum. Thellung described the taxon as a variety of Heracleum sphondylium (not Heracleum sibiricum) since he recognized Heracleum sphondylium subsp. sibiricum (L.) Simonk. (not Heracleum sibiricum L.). The typical form of Heracleum sibiricum has a glabrous ovary, whereas that of var. chaetocarpum has short, stiff, ascending hairs with pointy tips. The hairs are so short and sparse, they may not be visible to the naked eye. In 1961, the Polish botanist Maria Gawłowska described Heracleum sibiricum f. rarum, a form of var. chaetocarpum with elongated leaf lobes.

Distribution and habitat
Heracleum sibiricum is native to Europe and western Asia, ranging from France and Italy to western Siberia and Mongolia. For example, it occurs in northern and northeastern Poland but much less so in other parts of the country. Some authors claim its native range extends into Great Britain, while other sources suggest the taxon has been introduced in Britain. Authorities claim the taxon is widely introduced throughout North America, but, the presence of Heracleum sibiricum in eastern Canada and New England has not been confirmed.

Ecology
Heracleum sibiricum is most commonly a polycarpic perennial (not a biennial as often claimed), but approximately one-fourth of individuals are monocarpic. On average, first flowering requires 6–7 years of vegetative growth and may be delayed for up to 10 years. Although two or three (up to eight) subsequent flowerings are expected, most individuals do not flower in successive seasons. Estimates of average life span range from 12 to 16 years with a maximum age of 25 years.

Conservation
, the global conservation status of Heracleum sphondylium subsp. sibiricum (a synonym for Heracleum sibiricum) is unranked.