Centaurea maculosa

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

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

Centaurea maculosa, the spotted knapweed, is a species of Centaurea native to eastern Europe.

It has been introduced to North America,[1] where it is considered an invasive plant species in much of the western United States and Canada.[2] In 2000, C. maculosa occupied more than 7 million acres (28,000 km2) in the US.[2]

Knapweed is a pioneer species found in recently disturbed sites or openings. Once it has been established at a disturbed site, it continues to spread into the surrounding habitat. This species outcompetes natives through at least three methods:

  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. It is also suspected to be allelopathic, releasing a toxin from its roots that stunts the growth of nearby plants of other species.

Its seed is an achene about a quarter of an inch long with a small bristly pappus at the tip which makes the wind its primary means of dispersal. The leaves are a pale grayish-green. They are covered in fine short hairs. The lower leaves arrange a basal rosette, alternate, up to 6 inches (150 mm) long, deeply divided into lobes. Stem leaves less lobed progressively getting smaller toward the top. The stem is erect or ascending, slender, hairy and branching, which can grow up to three feet tall.

Contents

Biocontrol

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.[3] But in general, biocontrol has not been shown to be effective against C. maculosa [4]. In some instances, root-herbivory on C. maculosa stimulates additional release of catechin, the main allelopathic chemical which the species emits.[5]

Allelopathy via catechin

C. maculosa roots exude a substance called (-)-catechin, another stereoisomer of catechin[6], It acts as an herbicide to inhibit competition by a wide range of other plant species[7]. This phytotoxic compound inhibits seed germination and growth in making phosphorus more available in certain soils. It leads to cell death of competing plants by acidification of the cytoplasm. Some natives, such as Gaillardia grandiflora and Lupinus sericeus, are resistant to catechin-induced toxicity. This resistance is conferred by these plants' ability to produce oxalate.[6] Furthermore, native grasses grown in conjunction with oxalate-producing plants benefited from presence of oxalate.

References

  1. ^ Mauer, T., Russo, M.J., and Evans, M. (2001). Element stewardship abstract for Centaurea maculosa, spotted knapweed. The Nature Conservancy. Retrieved online: 14 July 2007.
  2. ^ a b Zouhar, Kris. ((2001, July).). "Centaurea maculosa. In: Fire Effects Information System, [Online"]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). http://www.fs.fed.us/database/feis/plants/forb/cenmac/all.html. Retrieved 2010, January 8. 
  3. ^ A.C. Blair (2008). "How do biological control and hybridization affect enemy escape?". Biological Control. http://lamar.colostate.edu/~hufbauer/Articles/Blairetal2008_Biological_Control.pdf. 
  4. ^ Mueller-Scharer, H.A. & Schroeder, D. (1993). The biological control of Centaurea spp. in North America: do insects solve the problem? Pest. Sci., 37, 343–353.
  5. ^ Giles C. Thelen (2005). "Insect herbivory stimulates allelopathic exudation by an invasive plant and the suppression of natives". Ecology Letters. http://www.leopold.wilderness.net/pubs/541.pdf. 
  6. ^ a b Tiffany L. Weir (2005). "Oxalate contributes to the resistance of Gaillardia grandiflora and Lupinus sericeus to a phytotoxin produced by Centaurea maculosa". Planta. http://plantecology.dbs.umt.edu/Full%20text%20papers%20and%20abstracts/2006%20papers/Oxalate%20paperWeir2006Planta.pdf. 
  7. ^ Bais HP, Walker TS, Stermitz FR, Hufbauer RA, Vivanco JM (April 2002). "Enantiomeric-dependent phytotoxic and antimicrobial activity of (±)-catechin. A rhizosecreted racemic mixture from spotted knapweed". Plant Physiol. 128 (4): 1173–9. doi:10.1104/pp.011019. PMID 11950966. http://www.plantphysiol.org/cgi/content/full/128/4/1173. 

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