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 the United States, and particularly widespread in dryer regions of the West, which has a similarly dry climate as the Mediterranean. This species along with Centaurea diffusa are a tumbleweed—breaking off at the top of the roots which facilitates the dispersal of its seeds.

Spotted knapweed
Scientific classification
Kingdom:
Plantae
(unranked):
Angiosperms
(unranked):
Eudicots
(unranked):
Asterids
Order:
Asterales
Family:
Asteraceae
Tribe:
Cynareae
Genus:
Centaurea
Species:
C. stoebe
Binomial name
Centaurea stoebe
Synonyms

Centaurea beibersteinii (lapsus)
Centaurea biebersteinii (Jaub. et Spach) Walp.

Description and habitat

This biennial or short-lived perennial plant usually has a stout taproot and/or pubescent stems when young. It has pale, deeply-lobed leaves, covered in fine short hairs. First year plants produce a basal rosette, alternate, up to 6 inches (150 mm) 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. The plant grows on stream banks, pond shorelines, sand prairies, old fields and pastures, roadsides, and along railroads, and many open, disturbed areas.

Invasive plant

It has been introduced to North America,[5] where it is considered an invasive plant species in much of the western United States and Canada.[6] In 2000, C. maculosa occupied more than 7 million acres (28,000 km2) in the US.[6]

Knapweed is a pioneer species found in recently disturbed sites or openings. As such, human disturbance is a major cause of infestations. Knapweed readily establishes itself and quickly expands in places of human disturbance such as industrial sites,[7] 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.[8] This species is believed to have several traits that contribute to its extreme competitive ability:

  1. A tap root that sucks up water faster than the root systems of its neighbors,
  2. Quick spread through high seed production, and
  3. Low palatability, meaning it is less likely to be chosen as food by herbivores.
  4. It is suspected to be allelopathic, releasing a toxin from its roots that stunts the growth of nearby plants of other species.

History in North America
Centaurea stoebe ssp. 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.[9] In the year 2000 it was reported in 45 of the 50 states in the US.[10] Spotted knapweed primarily affects rangelands of the northwest United States and Canada.[10] A 1996 study estimated the direct plus secondary economic impact of spotted knapweed in Montana to be approximately $42 million annually.[11] When spotted knapweed replaces native grasses, soil erosion and surface runoff are increased,[12] 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."[13]

Catechin controversy

The roots of C. 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.[14] 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. maculosa.[15][16] 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.[17][18] 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.[18]

Control

Biocontrol
Centaurea maculosa

Thirteen biological pest control agents have been used against this plant and its cogener, diffuse knapweed, including the moths Agapeta zoegana and Metzneria paucipunctella, the weevils Bangasternus fausti, Larinus obtusus, and Larinus minutus and Cyphocleonus achates, and the fruit flies Chaetorellia acrolophi, Urophora affinis and Urophora quadrifasciata.[19] But in general, biocontrol has not been shown to be effective against C. maculosa.[20] In some instances, root-herbivory on C. maculosa stimulates additional release of catechin, the main allelopathic chemical which the species emits.[21] In addition, moderate levels of herbivory by biocontrol agents can cause compensatory growth.[22]

Prescribed grazing

Prescribed grazing may be an effective means of controlling infestations. All growth forms are nutritious to sheep. High-density infestations can be controlled by fencing in the control area with sheep until the desired level of removal is achieved.[23]

Nomenclature

The common name spotted knapweed most often refers to Centaurea maculosa; however, inconsistencies exist in the scientific community. Two cytotypes of the plant exist which have been named as either different species or subspecies.[24] Centaurea maculosa has been used to describe the diploid and tetraploid form, however the diploid form has been called Centaurea stoebe which, having been published before C. maculosa, is the correct name for the species and the tetraploid form Centaurea biebersteinii.[24]

References
  1. https://www.biolib.cz/en/taxon/id41528/
  2. itis.gov
  3. "Centaurea stoebe in Tropicos".
  4. Somers, Paul (2008). A guide to invasive plants in Massachusetts. Massachusetts Division of fisheries and Wildlife. p. 39.
  5. 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.
  6. Zouhar, Kris. (July 2001). "Centaurea maculosa". Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Retrieved January 8, 2010.
  7. 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.
  8. DiTomasso, J.M. (2000). "Invasive weeds in rangelands: Species, impacts, and management" (PDF). Weed Management. 48 (2): 255–265. doi:10.1614/0043-1745(2000)048[0255:IWIRSI]2.0.CO;2. hdl:10365/3250.
  9. 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.
  10. Zouhar, Kris. "Centaurea maculosa". U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.
  11. Hirsch, S. A.; J. A. Leitch (1996). "The Impact of Knapweed on Montana's Economy". Agricultural Economics.
  12. 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.
  13. Erickson, David (2015-10-18). "Feds want to help Montana save honeybee populations, production". Missoulian. Retrieved 2015-10-19.
  14. Tiffany L. Weir (2005). "Oxalate contributes to the resistance of Gaillardia grandiflora and Lupinus sericeus to a phytotoxin produced by Centaurea maculosa" (PDF). Planta. Archived from the original (PDF) on 2010-06-21.
  15. Brendan Borrell. "NSF investigation of high-profile plant retractions ends in two debarments". Retraction Watch. Retrieved 29 November 2020.
  16. Shannon Palus. "Sample tampering leads to plant scientist's 7th retraction". Retraction Watch. Retrieved 29 November 2020.
  17. 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.
  18. 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.
  19. A.C. Blair (2008). "How do biological control and hybridization affect enemy escape?" (PDF). Biological Control. Archived from the original (PDF) on 2010-08-08.
  20. 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.
  21. Giles C. Thelen (2005). "Insect herbivory stimulates allelopathic exudation by an invasive plant and the suppression of natives" (PDF). Ecology Letters.
  22. 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.
  23. 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.
  24. 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.
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