synonym
A synonym is a word, morpheme, or phrase that means exactly 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 all ...
''Acroptilon repens'', with the common name Russian knapweed, is a 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 ho ...
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 the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago a ...
, Russian knapweed was introduced into
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
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) an ...
, Repin, in the plant is likely responsible for this toxicity.
Taxonomy
The species was first described by
Carl Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
in 1763 as ''Centaurea repens''.
Augustin Pyramus de Candolle
Augustin Pyramus (or Pyrame) de Candolle (, , ; 4 February 17789 September 1841) was a Swiss botanist. René Louiche Desfontaines launched de Candolle's botanical career by recommending him at a herbarium. Within a couple of years de Candol ...
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 reg ...
'' 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. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectivel ...
support separating 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 reg ...
''. 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
''Rhaponticum'' is a genus of flowering plants in the tribe Cardueae within the family Asteraceae.
Description
''Rhaponticum'' species are perennial herbaceous plants with simple, rarely branched stems. The leaves are simple to pinnatifid. T ...
'', a placement recognized by
The Plant List
The Plant List was a list of botanical names of species of plants created by the Royal Botanic Gardens, Kew and the Missouri Botanical Garden and launched in 2010. It was intended to be a comprehensive record of all known names of plant species ...
where this species is called ''Rhaponticum repens''.
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. Located ...