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Acroptilon repens (L.) DC.
Russian knapweed is probably top-killed by fire, while the roots are likely to remain unharmed. It is not known how Russian knapweed seeds are affected by exposure to heat. Research is needed in this area.
Russian knapweed is generally avoided by grazing animals due to its bitter taste . Prolonged ingestion (more than 30 to 60 days) of Russian knapweed by horses causes a fatal neurological disorder, nigropallidal encephalomalacia, when cumulative plant quantities of 60% to 200% of the animal's body weight are consumed [52,57].
Examination of feeding sites and analysis of rumen contents indicate some use of Russian knapweed by white-tailed deer in north-central Montana in the summer and winter months . Russian knapweed is considered important forage for Rocky Mountain bighorn sheep in British Columbia . Birds and rodents eat the seeds .
More info for the terms: fire exclusion, fire regime, frequency, fuel, presence, severity
Fire adaptations: Information regarding fire adaptations of Russian knapweed is not available in the literature. Russian knapweed has a deep-seated, extensive perennial root system that is likely to allow it to survive even severe fire, depending on site conditions. Russian knapweed is also capable of establishing from seed; however, the tolerance of the seeds to heating is unknown, and seed dispersal over any distance larger than the height of the plant requires a dispersal agent [2,58]. It is not known whether Russian knapweed is likely to establish from seed after fire.
FIRE REGIMES: Russian knapweed occurs primarily in agricultural communities in the western U.S. and southwestern Canada, where historic FIRE REGIMES have been dramatically altered. The historic FIRE REGIMES of the more native communities in which Russian knapweed sometimes occurs are of varied frequency and severity. Russian knapweed did not occur in these communities at the time in which historic FIRE REGIMES were functioning, but has established since fire exclusion began. It is unclear how historic FIRE REGIMES might affect Russian knapweed populations. It is also unclear how the presence of Russian knapweed might affect these fire regimes. Dense infestations of Russian knapweed may change the fire regime by changing the fuel characteristics and fire return interval at a given site. Research in this area is needed.
The following table provides some fire regime intervals for communities and ecosystems in which Russian knapweed may be found:
|Community or Ecosystem||Dominant Species||Fire Return Interval Range (years)|
|sagebrush steppe||Artemisia tridentata/Pseudoroegneria spicata||20-70 |
|basin big sagebrush||A. tridentata var. tridentata||12-43 |
|mountain big sagebrush||A. t. var. vaseyana||15-40 [5,15,46]|
|Wyoming big sagebrush||A. t. var. wyomingensis||10-70 (40**) [79,89]|
|saltbush-greasewood||Atriplex confertifolia-Sarcobatus vermiculatus|
|desert grasslands||Bouteloua eriopoda and/or Pleuraphis mutica||5-100|
|plains grasslands||B. spp.|
|blue grama-needle-and-thread grass-western wheatgrass||B. gracilis-Hesperostipa comata-Pascopyrum smithii||53]|
|curlleaf mountain-mahogany*||Cercocarpus ledifolius||13-1000 [6,65]|
|mountain-mahogany-Gambel oak scrub||C. l.-Quercus gambelii|
|western juniper||Juniperus occidentalis||20-70|
|Rocky Mountain juniper||J. scopulorum|
|mountain grasslands||Pseudoroegneria spicata||3-40 (10**) [3,4]|
*fire return interval varies widely; trends in variation are noted in the species summary
Russian knapweed is avoided by grazing animals due to its bitter taste. It is so
bitter that as little as 0.01%
contamination by weight reduces the quality of flour and other grain products .
More info for the terms: adventitious, involucre, monoecious, pappus
Russian knapweed reproduces by seed and by adventitious buds on horizontally spreading roots. Since Russian knapweed produces relatively few seeds and lacks effective mechanisms for seed dispersal, local infestations increase primarily by adventitious roots [61,83,86].
Breeding system: Russian knapweed is monoecious and is an obligate outcrosser .
Pollination: Russian knapweed is insect pollinated [36,83].
Seed production: A single Russian knapweed plant can produce about 1,200 seeds per year (Ivanova 1966, as cited by [83,86]). Watson  reported Russian knapweed seed production of about 100 seeds per plant per year along roadsides, and about 292 seeds per plant on rangeland in British Columbia, with a high ovule abortion rate. Beck  reports seed production of about 50 to 500 per shoot in Colorado. Flower production declines with decreasing light levels .
Seed dispersal: Russian knapweed seedheads generally remain closed at maturity, and the relatively heavy seeds tend to lose the small pappus bristles at maturity; therefore, wind dispersal is an unlikely method for long-range seed dispersal [58,83]. Ballistic dispersal may be more important than wind dispersal: Mature achenes dehisce from the receptacle and usually remain in the involucre, but can be launched over distances roughly equal to the height of the plant when the involucre sways in a breeze . The primary means of long-range seed dispersal is probably via contaminated hay and other seed (primarily alfalfa), or by movement of farm machinery or other vehicles [58,61].
Seed banking: Seed banking of Russian knapweed is not reported in the literature. It is unclear how long Russian knapweed seeds can remain viable, as reports vary from 2 to 3 years (Ivanova 1966 as cited by ), while Andersen (1968) reported successful germination after 5 years of dry storage , and Selleck  reported successful germination of seeds after up to 9 years storage at room temperature.
Germination: Russian knapweed seeds do not germinate readily , and germination rarely occurs in the field [66,83]. An initial dormancy period has been observed in Russian knapweed seeds and can be broken by alternating temperatures. Russian knapweed seeds are able to germinate under a wide range of temperatures (33 to 95 Â°F (0.5-35 °C)) with optimum germination occurring between 68 and 86 Â°F (20-30 °C) (, and sources therein). Light is not essential for germination, but alternating light and darkness improves germination, and white light appears to stimulate germination .
Seedling establishment/growth: No information
Asexual regeneration: Russian knapweed reproduces primarily by vegetative means, and can spread rapidly and form dense colonies. The root system consists of the taproot, 1 to many horizontal roots, and their vertical extensions. Buds on the horizontal roots can form adventitious shoots that can grow to be independent plants ([58,83,86] and sources therein). Spread can be hastened by cultivation .
Acroptilon repens has been reported also from Arkansas, Illinois, Indiana, Kentucky, Louisiana, Michigan, Missouri, New York, Ohio, Virginia, and Wisconsin; I have not seen specimens from those states.
Acroptilon repens is a serious weed pest, especially in the western United States. It is a strong competitor in infested areas, often forming dense colonies, and has allelopathic effects on other plants growing nearby. It is very difficult to control or eradicate once it becomes established. It reproduces vigorously from seed and spreads from adventitious buds borne on deep-seated runner roots. Root fragments readily regenerate as new individuals after cultivation. In addition, Russian knapweed is very poisonous to horses, causing neurological symptoms. Because of its bitter taste, it is usually avoided by grazing animals, and consequently it tends to spread when more palatable plants are consumed.
|Rights holder/Author||eFloras.org Copyright © Missouri Botanical Garden|
Russian knapweed (Rhaponticum repens, synonym Acroptilon repens) is a bushy rhizomatous perennial, up to 8 dm 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, 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, 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.
The species was first described by Carl Linnaeus in 1763 as Centaurea repens.Augustin Pyramus de Candolle separated it from the genus Centaurea 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 study, the structure of the flower, and the chromosome number support separating it from the genus Centaurea. 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, a placement recognized by The Plant List where this species is called Rhaponticum repens.
- ^ a b "The Plant List: A Working List of All Plant Species". Retrieved 3 October 2014.
- ^ "Acroptilon repens". Flora of North America.
- ^ "Centaurea repens". The Plant List. Retrieved 2015-02-26.
- ^ a b "IPNI Plant Name Query Results for Centaurea repens". The International Plant Names Index. Retrieved 2015-02-26.
- ^ Carl Linnaeus (1763). "Centaurea 28 repens". Species plantarum :exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas 2 (2 ed.). p. 1293.
- ^ a b "Acroptilon". Flora of North America.
- ^ Hidalgo, Oriane; Garcia-Jacas, Núria; Garnatje, Teresa & Susanna, Alfonso (2006), "Phylogeny of Rhaponticum (Asteraceae, Cardueae–Centaureinae) and Related Genera Inferred from Nuclear and Chloroplast DNA Sequence Data: Taxonomic and Biogeographic", Annals of Botany 97 (5): 705–714, doi:10.1093/aob/mcl029
- ^ "Rhaponticum repens". The Plant List. Retrieved 2015-02-26.
More info on this topic.
More info for the terms: geophyte, hemicryptophyte
RAUNKIAER  LIFE FORM:
The currently accepted scientific name of Russian knapweed is Acroptilon repens
(L.) DC. (Asteraceae) [37,39,40,84].
Regularity: Regularly occurring
Regularity: Regularly occurring