Centaurea stoebe

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Spotted knapweed
Centaurea maculosa Bozeman.jpg
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Asterales
Family: Asteraceae
Genus: Centaurea
C. stoebe
Binomial name
Centaurea stoebe

Centaurea stoebe, the spotted knapweed or panicled knapweed,[1] is a species of Centaurea native to eastern Europe.[2][3] It is also an invasive species in southern Canada, and northwestern Mexico, and nearly every state in the United States; it has thrived in the western United States in particular, much of which has a dry climate similar to the Mediterranean. This species and Centaurea diffusa are tumbleweeds — plants that break free of their roots and tumble in the wind, facilitating the dispersal of their seeds.[citation needed]


Centaurea stoebe is a biennial or short-lived perennial plant, and it usually has a stout taproot and pubescent stems when young. It has pale and deeply-lobed leaves covered in fine short hairs. First-year plants produce a basal rosette, alternate, up to 6 inches (15 cm) long, deeply divided into lobes.[4] It produces a stem in its second year of growth. Stem leaves are progressively less lobed, getting smaller toward the top. The stem is erect or ascending, slender, hairy and branching, and can grow up to three feet tall. The flowers are a vibrant pink flowers with black-tipped sepals that look like spots, which is the origin of its common name. The fruit is an achene (about a quarter-inch long) with a short, bristly pappus. It is primarily dispersed by wind.[citation needed]


The common name spotted knapweed most often refers to Centaurea stoebe, formerly known as C. maculosa; however, there is some confusion surrounding the taxonomy of this genus. Two[specify] cytotypes of C. stoebe exist which have been considered as different species by some taxonomists. The diploid form of the plant is now called Centaurea stoebe L. spp. stoebe, while the tetraploid is known as C. stoebe L. spp. micranthos or by some taxonomists as C. biebersteinii DC.[5]

Distribution and habitat[edit]

The plant grows on stream banks, pond shorelines, sand prairies, old fields and pastures, roadsides, along railroads, and in many open and disturbed areas.[citation needed]


Centaurea stoebe has been introduced to North America,[6] where it is considered an invasive plant species in much of the western United States and Canada. In 2000, C. stoebe occupied more than 7 million acres (28,000 km2) in the US.[7]

Spotted knapweed is a pioneer species found in recently disturbed sites or openings. As such, human disturbance is a major cause of infestations. It readily establishes itself and quickly expands in places of human disturbance such as industrial sites,[8] along roadsides, and along sandy riverbanks. Once established, it also has the potential to spread into undisturbed natural areas.[4] Because cattle prefer the native bunchgrass over knapweed, overgrazing can often increase the density and range of knapweed infestations.[9] This species is believed to have several traits that contribute to its extreme competitive ability:[citation needed]

  1. A tap root that sucks up water faster than the root systems of its neighbors.
  2. Rapid dispersal through high seed production.
  3. Low palatability, making it less likely to be eaten.
  4. Its purported allelopathy allows it to thrive by stunting the growth of neighboring plants.

History in North America[edit]

Centaurea stoebe subsp. micranthos in East Wenatchee, Douglas County, Washington

Spotted knapweed likely spread to North America in an alfalfa shipment. It was first recorded in Bingen, Klickitat County, Washington in the late 1800s. By 1980, it had spread to 26 counties in the Pacific Northwest.[10] In the year 2000, it was reported in 45 of the 50 states in the United States. Spotted knapweed primarily affects rangelands of the northwest United States and Canada.[11] A 1996 study estimated the direct plus secondary economic impact of spotted knapweed in Montana to be approximately $42 million annually.[12] When spotted knapweed replaces native grasses, soil erosion and surface runoff are increased,[13] depleting precious soil resources.

In 2015, a Missoula, Montana beekeeper whose bees rely on local knapweed stated that "knapweed produces great honey ... people should consider planting native wildflowers instead of just taking out weeds."[14]

Catechin controversy[edit]

The roots of Centaurea stoebe exude (-)-catechin, which has been proposed to function as a natural herbicide that may inhibit competition by a wide range of other plant species.[15] While this phytotoxic compound can inhibit seed germination and growth at high concentrations, it is debated whether concentrations in field soils are high enough to affect competition with neighboring plants. Several high-profile papers arguing for the importance of catechin as an allelochemical were retracted after it was found that they contained fabricated data showing unnaturally high levels of catechin in soils surrounding C. stoebe.[16][17] Subsequent studies from the original lab have not been able to replicate the results from these retracted studies, nor have most independent studies conducted in other laboratories.[18][19] Thus, it is doubtful whether the levels of (-)-catechin found in soils are high enough to affect competition with neighboring plants. The proposed mechanism of action (acidification of the cytoplasm through oxidative damage) has also been criticized, on the basis that (-)-catechin is actually an antioxidant.[19]


An 8-year study in Michigan found that restoring native plant communities in knapweed-infested sites requires multi-faceted and multi-year approaches. This includes an initial site preparation by mowing and an optional application of a clopyralid or glyphosate herbicide followed by reseeding with the desired plant communities. Yearly hand pulling of C. stoebe over the course of the study virtually eradicated the infestation. Burning treatments of infested sites reduced the labour needs for pulling and encouraged native plant community establishment.[20]

Another study over 3 years comparing the effectiveness of different combinations of annual spring, summer, and fall mowing treatments recommends an annual fall mowing during the flowering or seed-production stage in controlling C. stoebe infestations.[21]


Centaurea stoebe

Thirteen biological pest control agents have been used against this plant and its congener, diffuse knapweed (Centaurea diffusa), including the moths, Agapeta zoegana and Metzneria paucipunctella; the weevils, Bangasternus fausti, Larinus obtusus, Larinus minutus and Cyphocleonus achates; and the fruit flies, Chaetorellia acrolophi, Urophora affinis and Urophora quadrifasciata.[22] But in general, biocontrol has not been shown to be effective against C. stoebe.[23] In some instances, root-herbivory on C. stoebe stimulates additional release of catechin, which may function as an allelopathic toxin.[24] In addition, moderate levels of herbivory by biocontrol agents can cause compensatory growth.[25]

Prescribed grazing[edit]

Prescribed grazing may be an effective means of controlling infestations, as all growth forms of C. stoebe are nutritious to sheep. High-density infestations can be controlled by fencing in the affected area with sheep until the desired level of removal is achieved.[26]


  1. ^ "Taxon profile: Spotted Knapweed - Centaurea stoebe L." BioLib: Biological library.
  2. ^ itis.gov
  3. ^ "Centaurea stoebe in Tropicos".
  4. ^ a b Somers, Paul (2008). A guide to invasive plants in Massachusetts. Massachusetts Division of Fisheries and Wildlife. p. 39.
  5. ^ Blair, Amy; Nissen, Scott J.; Hufbauer, Ruth A.; Brunk, Galen R. (September 2006). "A lack of evidence for an ecological role of the putative allelochemical (±)-Catechin in Spotted Knapweed". Journal of Chemical Ecology. 32 (10): 2327–2331. doi:10.1007/s10886-006-9168-y. PMID 16955253. S2CID 2450684.
  6. ^ Mauer, T., Russo, M.J., and Evans, M. (2001). Element stewardship abstract for Centaurea maculosa, spotted knapweed Archived November 1, 2006, at the Wayback Machine. The Nature Conservancy. Retrieved online: 14 July 2007.
  7. ^ Zouhar, K. (July 2001). "Centaurea maculosa". Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Retrieved 2010-01-08.
  8. ^ Guobis, Thomas Joseph (1980). Link immigration and establishment of Centaurea maculosa Lam. in a central New York limestone quarry (M.S. Thesis). State University of New York, College of Environmental Science and Forestry.
  9. ^ DiTomasso, J.M. (2000). "Invasive weeds in rangelands: species, impacts, and management" (PDF). Weed Science. 48 (2): 255–265. doi:10.1614/0043-1745(2000)048[0255:IWIRSI]2.0.CO;2. hdl:10365/3250. ISSN 0043-1745.
  10. ^ Roger L. Sheley; James S. Jacobs; Michael F. Carpinelli (April–June 1998). "Distribution, Biology, and Management of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed (Centaurea maculosa)". Weed Technology. 12 (2): 353–362. doi:10.1017/S0890037X00043931.
  11. ^ Zouhar, K. "Centaurea maculosa". U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.
  12. ^ Hirsch, S.A.; Leitch, J.A. (1996). "The impact of knapweed on Montana's economy". Agricultural Economics.
  13. ^ John R. Lacey; Clayton B. Marlow; John R. Lane (1989). "Influence of spotted knapweed (Centaurea maculosa) on surface runoff and sediment yield" (PDF). Weed Technology. 3 (4): 627–631. doi:10.1017/S0890037X00032929. S2CID 81635854. Archived from the original (PDF) on 2020-02-25.
  14. ^ Erickson, David (2015-10-18). "Feds want to help Montana save honeybee populations, production". Missoulian. Retrieved 2015-10-19.
  15. ^ Tiffany L. Weir (2005). "Oxalate contributes to the resistance of Gaillardia grandiflora and Lupinus sericeus to a phytotoxin produced by Centaurea stoebe" (PDF). Planta. Archived from the original (PDF) on 2010-06-21.
  16. ^ Brendan Borrell (2 September 2015). "NSF investigation of high-profile plant retractions ends in two debarments". Retraction Watch. Retrieved 29 November 2020.
  17. ^ Shannon Palus (3 March 2016). "Sample tampering leads to plant scientist's 7th retraction". Retraction Watch. Retrieved 29 November 2020.
  18. ^ Perry, L. G., G. C. Thelen, W. M. Ridenour, R. M. Callaway, M. W. Paschke, and J. M. Vivanco. 2007. Concentrations of the Allelochemical (+/-)-catechin IN Centaurea maculosa soils. J Chem Ecol 33:2337–2344.
  19. ^ a b Duke, S.O., F.E. Dayan, J. Bajsa, K.M. Meepagala, R.A. Hufbauer, and A.C. Blair. 2009. The case against (–)-catechin involvement in allelopathy of Centaurea stoebe (spotted knapweed). Plant Signaling & Behavior 4:422–424. Taylor & Francis.
  20. ^ MacDonald, Neil W.; Dykstra, Kaitlyn M.; Martin, Laurelin M. (2019-03-04). Marrs, Rob (ed.). "Restoration of native‐dominated plant communities on a Centaurea stoebe‐infested site". Applied Vegetation Science. Wiley Publishing. 22 (2): 300–316. doi:10.1111/avsc.12427. ISSN 1402-2001.
  21. ^ Rinella, Matthew J.; Jacobs, James S.; Sheley, Roger L.; Borkowski, John J. (2001). "Spotted knapweed response to season and frequency of mowing". Journal of Range Management. JSTOR. 54 (1): 52. doi:10.2307/4003527. hdl:10150/643834. ISSN 0022-409X. JSTOR 4003527.
  22. ^ Blair, A.C. (2008). "How do biological control and hybridization affect enemy escape?" (PDF). Biological Control. Archived from the original (PDF) on 2010-08-08.
  23. ^ Mueller-Scharer, H.A.; Schroeder, D. (1993). "The biological control of Centaurea spp. in North America: do insects solve the problem?". Pesticide Science. 37 (4): 343–353. doi:10.1002/ps.2780370407.
  24. ^ Giles C. Thelen (2005). "Insect herbivory stimulates allelopathic exudation by an invasive plant and the suppression of natives" (PDF). Ecology Letters.
  25. ^ Callaway, R.M.; DeLuca, T.H.; Belliveau, W.M. (1999). "Biological-Control Herbivores May Increase Competitive Ability of the Noxious Weed Centaurea maculosa". Ecology. 80 (4): 1196–1201. doi:10.2307/177067. JSTOR 177067.
  26. ^ Frost, R.A.; Launchbaugh, K.L. (2003). "Prescription Grazing for Rangeland Weed Management: A New Look at an Old Tool". Rangelands. doi:10.2458/azu_rangelands_v25i6_frost.

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