''Rhaponticum repens'',

synonyms A synonym is a word, morpheme, or phrase that means precisely or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are a ...

including ''Acroptilon repens'' and ''Leuzea repens'', with the common name Russian knapweed, is a species of bushy

rhizomatous In botany and dendrology, a rhizome ( ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

perennial, up to 80 cm tall. Stems and leaves are finely arachnoid-tomentose becoming glabrous and green with age. The rosette leaves are oblanceolate, pinnately lobed to entire, 2–3 cm wide by 3–8 cm long. The lower cauline leaves are smaller, pinnately lobed; the upper leaves become much reduced, sessile, serrate to entire. The heads are numerous terminating the branches. Flowers are pink to purplish, the marginal ones not enlarged. The outer and middle involucral bracts are broad,

striate In geology, a striation is a groove, created by a geological process, on the surface of a rock or a mineral. In structural geology, striations are linear furrows, or linear marks, generated from fault movement. The striation's direction revea ...

, smooth with broadly rounded tips; the inner bracts are narrower with hairy tips. Pappus present with bristles 6–11 mm long. Fruit is a whitish, slightly ridged achene. Russian knapweed is a deep-rooted long-lived perennial. Some stands have been in existence for 75 years. It forms dense colonies in cultivated fields, orchards, pastures, and roadsides. A native to

Eurasia Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...

, Russian knapweed was introduced into North America in the late 19th century. Absent only from southeastern U.S., it has become widespread in other regions, especially in the western United States. Nigropallidal encephalomalacia, also called ''chewing disease'', a movement disorder similar to Parkinson's disease, is caused in horses ingesting Russian knapweed for prolonged periods. A

sesquiterpene lactone Sesquiterpene lactones (SLs) are a class of sesquiterpenoids that contain a lactone ring. They are most often found in plants of the family Asteraceae (daisies, asters). Other plant families with SLs are Umbelliferae (celery, parsley, carrots) ...

, repin, in the plant is likely responsible for this toxicity. Acroptilon repens absnd

Taxonomy

The species was first described by

Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

in 1763 as ''Centaurea repens''.

Augustin Pyramus de Candolle Augustin Pyramus (or Pyrame) de Candolle (, , ; 4 February 17789 September 1841) was a Swiss people, Swiss botany, botanist. René Louiche Desfontaines launched de Candolle's botanical career by recommending him at a herbarium. Within a couple ...

separated it from the genus ''

Centaurea ''Centaurea'' () is a genus of over 700 species of herbaceous thistle-like flowering plants in the family Asteraceae. Members of the genus are found only north of the equator, mostly in the Eastern Hemisphere; the Middle East and surrounding ...

'' in 1838, placing it in the genus ''Acroptilon''. The genus name derives from ''acro-'' (high, here meaning tip) and ''ptilo-'' (feather). A 1995

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

study, the structure of the flower, and the

chromosome number Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

support separating it from the genus ''

''. Some sources then continue to place it as the sole member of the monotypic genus ''Acroptilon''. A phylogenetic study published in 2006 concluded that ''Acroptilon'' belongs in the genus ''Rhaponticum''.

References

External links

Jepson Manual TreatmentSpecies Profile- Russian Knapweed (''Rhaponticum repens'')
National Invasive Species Information Center,

United States National Agricultural Library The United States National Agricultural Library (NAL) is one of the world's largest agricultural research libraries, and serves as a national library of the United States and as the library of the United States Department of Agriculture. Locate ...

. Lists general information and resources for Russian Knapweed. {{Taxonbar, from1=Q15551896, from2=Q89024824, from3=Q12846085, from4=Q25531399 Cardueae Flora of temperate Asia Flora of Europe Plants described in 1763