Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Centaurea macrocephala
(giant knapweed)



Centaurea macrocephala (giant knapweed)


  • Last modified
  • 07 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Centaurea macrocephala
  • Preferred Common Name
  • giant knapweed
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • C. macrocephala is a robust perennial that has been in cultivation for over 200 years. It was reportedly introduced to the UK in 1805 and its presence in the USA dates back to at least 812, when Thomas Jefferson...

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Centaurea macrocephala; plants in meadow. Note size.
CaptionCentaurea macrocephala; plants in meadow. Note size.
Copyright©Cindy Roché
Centaurea macrocephala; plants in meadow. Note size.
HabitCentaurea macrocephala; plants in meadow. Note size.©Cindy Roché
Centaurea macrocephala; flower head.
CaptionCentaurea macrocephala; flower head.
Copyright©Cindy Roché
Centaurea macrocephala; flower head.
FlowerCentaurea macrocephala; flower head.©Cindy Roché
Centaurea macrocephala; bud scale.
TitleBud scale
CaptionCentaurea macrocephala; bud scale.
Copyright©Cindy Roché
Centaurea macrocephala; bud scale.
Bud scaleCentaurea macrocephala; bud scale.©Cindy Roché
Centaurea macrocephala; infestation and invasive habit.
CaptionCentaurea macrocephala; infestation and invasive habit.
Copyright©Cindy Roché
Centaurea macrocephala; infestation and invasive habit.
InfestationCentaurea macrocephala; infestation and invasive habit.©Cindy Roché


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Preferred Scientific Name

  • Centaurea macrocephala Puschkarew ex Willdenow, 1803

Preferred Common Name

  • giant knapweed

Other Scientific Names

  • Grossheimia macrocephala (Puschkarew ex Willdenow) Sosnowsky & Takhtajan, 1945

International Common Names

  • English: Armenian basketflower; big yellow centaurea; bighead knapweed; Bighead knapweed; big-headed knapweed; globe centaurea; globe cornflower; golden thistle; great golden knapweed; lemon fluff knapweed; yellow bachelor's button; yellow bachelor's cornflower; yellow hardhat; yellow hardhead; yellow thistle
  • French: centaurée a gros capitules

Local Common Names

  • Finland: keltakaunokki
  • Germany: Gelbe Riesen- Flockenblume; Grosskopfige Flockenblume
  • Sweden: gulklint

EPPO code

  • CENMC (Centaurea macrocephala)

Summary of Invasiveness

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C. macrocephala is a robust perennial that has been in cultivation for over 200 years. It was reportedly introduced to the UK in 1805 and its presence in the USA dates back to at least 812, when Thomas Jefferson grew it at Monticello from seeds from Philadelphia nurseryman, Bernard McMahon (Anon., 2009). It is still widely used in the horticultural trade. It is listed as a Class A noxious weed in Washington State, USA (USDA-NRCS, 2011) and is a prohibited noxious weed in Alberta, Canada (CIPM, 2011). It threatens natural meadows and spreads in disturbed areas and once established is difficult to control.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Asterales
  •                         Family: Asteraceae
  •                             Genus: Centaurea
  •                                 Species: Centaurea macrocephala

Notes on Taxonomy and Nomenclature

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The name C. macrocephala appears to be used worldwide, except in Russia where the genus name has been changed to Grossheimia (Garcia-Jacas et al., 2000).


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Perennial. 50-170 cm tall. Several to many erect stems from a woody, tap-rooted crown are unbranched or sparingly branched distally, villous with septate hairs, thinly arachnoid-tomentose, swollen below the capitula. Leaves are also short-villous and thinly arachnoid, ranging to almost glabrate, dotted with resinous glands. The basal and lower cauline leaves are borne on petioles; blades are oblanceolate to narrowly ovate, 10 to 30 cm, with entire or shallowly dentate margins. Cauline leaves are sessile, shortly decurrent, gradually becoming smaller up the stem, especially the cluster of leaves just below the heads; blades lanceolate to ovate, 5 to 10 cm long, margin entire or slightly undulate, apices acute. Heads subtended by a cluster of reduced leaves. Involucres ovoid to hemispheric, 25-35 mm, surrounded by 3 to 12 rows of layered phyllaries. Phyllary base (body) pale-green to straw-coloured, ovate to broadly lanceolate, glabrous; phyllary appendages erect to spreading, brown to golden, scarious, abruptly expanded forming a cup, 1-2 cm wide, normally concealing the basal parts, lacerate fringed, sometimes tipped by weak spines 1-2 mm, glabrous. Florets many; corollas yellow; corollas of sterile florets slightly expanded, ca. 4 mm; corollas of disc florets ca. 3.5 mm. Cypselae 7-8 mm; pappi of flattened bristles, 5-8 mm long (Roché, 1991; Keil and Ochsmann, 2006).

Plant Type

Top of page Broadleaved
Seed propagated
Vegetatively propagated


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C. macrocephala appears to be native only to the Caucasus region and the nearby Anatolia region in Turkey (Wagenitz, 1975). Previous reports of it in Romania are either erroneous, or perhaps it has naturalized from cultivation there, as it has in other parts of Europe (Kurtto and Lahti, 1987; Clement and Foster, 1994; Preston et al., 2002; Pysek et al., 2002). This species is widely cultivated and has been for a long time. Based on its native habitat and where it is cultivated, this species appears to be limited to temperate climates. It is so widely cultivated that therefore the ‘risk of introduction’ is very high. However, given that it has not become a widespread pest, it is not highly invasive. Nevertheless, it is not a species that should be ignored. There are numerous reports of its aggressive behaviour in the garden and locations where it has naturalized, on garden discussion groups online. Its horticultural distribution is apparently legal everywhere except in Washington State, USA, where it is illegal to buy, sell or offer it for sale (WSDA Plant Protection Division, 2008). According to USDA (2009), it is naturalized in 11 of the 39 counties in Washington State: Clallam; Whatcom; Skagit; King; Thurston; Lewis; Klickitat; Okanogan; Pend Oreille; Spokane; and Whitman. The reliability of these reports could not be independently validated for all counties. It is present in New Zealand, in the Christchurch Botanical Garden (C Roché, [address available from CABI], USA, personal communication, 2009).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes


ArmeniaPresentNativeWagenitz, 1975; Shoeb et al., 2004
AzerbaijanPresentNativeWagenitz, 1975
IranPresentNative Not invasive Shoeb et al., 2004
TurkeyPresentNativeWagenitz, 1975NE Anatolia: district of Ardahan (Yalnizcam area)

North America

CanadaUnconfirmed recordCAB Abstracts
-British ColumbiaPresentIntroduced Invasive Roché, 1991Quesnel
-OntarioPresentIntroducedKeil and Ochsmann, 2006
-QuebecPresentIntroducedKeil and Ochsmann, 2006
USAUnconfirmed recordCAB Abstracts
-ColoradoPresentIntroducedKeil and Ochsmann, 2006
-IdahoLocalisedIntroduced Invasive Rice, 2009Grangeville (Idaho County), 1995
-MontanaPresentIntroduced1976Rice, 2009Toole, Ravalli, Flathead counties
-OregonPresentIntroduced1947Roché and Talbott, 1986In cultivation
-WashingtonLocalisedIntroduced1918 Invasive Roché and Talbott, 1986; Roché, 1991; Rice, 2009; WTU, 2009King, Kittitas, Pend Oreille, Okanogan, Thurston, Whitman counties


Czech RepublicPresentPysek et al., 2002Casual alien
DenmarkPresentIntroducedAlanen et al., 2004Casual alien, cultivation escape
FinlandPresentIntroducedKurtto and Lahti, 1987Cultivation escape
UKPresentIntroducedClement and Foster, 1994; Preston et al., 2002Aggressive in cultivation (garden thug), naturalized


New ZealandPresentIn cultivation

History of Introduction and Spread

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It was first reported to be invasive in Washington State, USA where it is now listed as a Class A Noxious Weed under the Revised Code of Washington (Washington State Legislature, 1997). In 1979, a single naturalized plant was discovered and within 5 years had expanded to 5 ha (C Roché, [address available from CABI], USA, personal observation, 2009). By 1985, other naturalized populations were reported in Whitman and Okanogan counties, Washington, in Wyoming, and near Quesnel, British Columbia, Canada (Roché, 1991). In 1995 it was reported from a horse pasture near Grangeville, Idaho, USA (Rice, 2009). In addition to Washington and Idaho, it is recorded from Oregon, Montana, Ontario, Wisconsin, Michigan and Quebec (USDA, 2009), but whether these all represent naturalized populations is unknown. The occurrence in cultivation is clearly much more widespread (C Roché, USA, personal observation) based on the number of horticultural outlets that offer this species for sale, 2009).


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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Europe   Horticulture (pathway cause) Yes No From Caucasus region
USA Europe Horticulture (pathway cause) Yes No Early 1800s


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In its native range, C. macrocephala is reported to grow in subalpine meadows at 2000 to 2300 m.a.s.l. (Wagenitz, 1975) or in open places in forest of the upper mountain zone, in tall herbaceous communities (Klokov et al., 1963). In its naturalized range, it grows in moist temperate conditions that mostly would support forest vegetation as native cover, or in a few cases, native prairie. In North America, the habitat is reported as meadows and grassy clearings, 400 to 2000 m.a.s.l. (Keil and Ochsmann, 2006).

Habitat List

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Terrestrial – ManagedManaged grasslands (grazing systems) Present, no further details Harmful (pest or invasive)
Managed grasslands (grazing systems) Present, no further details Natural
Disturbed areas Present, no further details Harmful (pest or invasive)
Disturbed areas Present, no further details Natural

Hosts/Species Affected

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C. macrocephala has primarily invaded communities already dominated by perennial plants: meadows; pastures; bluegrass sod; and perennial grass openings in forested areas (Roché, 1991).

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Dactylis glomerata (cocksfoot)PoaceaeUnknown
Poa pratensis (smooth meadow-grass)PoaceaeUnknown

Biology and Ecology

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2n = 18, Russia (Keil and Ochsmann, 2006)
Reproductive Biology
C. macrocephala is a perennial that reproduces by seed. Gardeners and nursery workers may propagate it by dividing the crown. In naturalized populations, rosettes generally do not flower in the first year. Peak flowering is in mid- to late summer.


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Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Ds - Continental climate with dry summer Preferred Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)

Soil Tolerances

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Soil drainage

  • free

Soil reaction

  • acid
  • neutral

Soil texture

  • light
  • medium

Means of Movement and Dispersal

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When the cypselae mature, the capitula open widely to disperse the propagules, which are dislodged by wind, passing animals or vehicles. Although plumed, they are heavy so normally fall close to the parent plant unless carried by a vector (e.g. animals with rough fur or hair, or by lodging in a vehicle crevice). Long distance dispersal appears to be almost exclusively via horticultural commerce, sold either as seeds and plants or as dried capitula in floral arrangements.

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Mail Yes

Environmental Impact

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Once established, this species is very difficult to control, and is a threat to natural areas, including subalpine meadows (Washington State Noxious Weed Control Board, 1998). To date (2009), naturalized populations remain relatively small and isolated, but Pend Oreille County Weed Control Board, Washington State, USA has been actively trying to eradicate a 4 ha population for about 25 years (S Sorby, Pend Oreille County Weed Coordinator, USA, personal communication, 2009). Complete prevention of seed production has not been attained as of August 2009 and seedlings continue to appear each year.

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Benefits from human association (i.e. it is a human commensal)
  • Long lived
  • Has propagules that can remain viable for more than one year
Impact outcomes
  • Ecosystem change/ habitat alteration
Impact mechanisms
  • Competition - monopolizing resources
  • Competition - shading
Likelihood of entry/control
  • Highly likely to be transported internationally deliberately

Uses List

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  • Cut flower
  • Propagation material
  • Seed trade

Similarities to Other Species/Conditions

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This is by far the largest Centaurea in cultivation or naturalized, and would not be easily confused with any other species.

Prevention and Control

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Physical/mechanical control

In a garden setting, small seedlings may be pulled. C. macrocephala is a large, tap-rooted perennial, so pulling is impractical for large infestations. Plants may be dug with a shovel or other tool, but plants can re-sprout if the root is left intact (Washington State Noxious Weed Control Board, 2008). None of the sites in Washington, USA have been accessible for cultivation equipment, but plants would be killed by repeated cultivation. However, this would damage desired associated perennial vegetation (native and introduced pasture grasses). When the flowering stem is broken off, a new stem will grow from the woody crown, producing another flower head later in the season. Repeated mowing diminishes seed production and may eventually deplete root reserves. Small plants can be dug, but the site should be monitored until the seed bank is depleted.
Cattle will graze C. macrocephala, but the amount of use under normal conditions is not considered control. Sheep and goats may be more effective, but have not been studied.
Movement control
Long distance dispersal by sale of plants and seed is restricted only in Washington State. Quarantines could be established in other areas; so far only warnings have been issued.
Chemical control
C. macrocephala is susceptible to the same chemicals as other Centaurea species, including phenoxy acetic acid (2,4-D), benzoic acid (dicamba), pyridines (triclopyr, aminopyralid, clopyralid, picloram), imidazolinones (imazapic), semicarbazone (diflufenzopyr), and glyphosate. Recommended rates and application times are given for the Pacific Northwest states in the Pacific Northwest Weed Management Handbook (Peachey, 2009).


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Alanen A, Bongard T, Einarsson E, Hansen H, Hedlund L, Jansson K, Josefsson M, Philipp M, Sandlund OT, Svart AE, Svart HE, Weidema I, 2004. Introduced Species in the Nordic Countries (Denmark) under Nordic Council of Ministers (NMR), subgroup Natur-og Friluftslivsgruppen.

Anon, 2009. Thomas Jefferson, Monticello. Charlottesville, USA: Monticello and the Thomas Jefferson Foundation.

Bohlmann F, Layser J, 1970. Polyacetylenic compounds. 177. Constituents of Centaurea macrocephala Puschk. Chemische Berichte, 103(7):2100-2104

CIPM, 2011. Western States and Provinces Weed Lists. Bozeman, MT, USA: Montana State University.

Clement EJ, Foster MC, 1994. Alien plants of the British Isles. London, UK: Botanical Society of the British Isles, 603 pp

Crookston RK, Moss DN, 1970. The relation of carbon dioxide compensation and chlorenchymatous vascular bundle sheaths in leaves of dicots. Plant Physiology, 46:564-567

Daniela I, 1997. IOPB chromosome data 11. Newsletter of the International Organisation of Plant Biosystems (Oslo), 26/27:14

Font M, Garcia-Jacas N, Vilatersana R, Roquet C, Susanna A, 2009. Evolution and biogeography of Centaurea section Acrocentron inferred from nuclear and plastid DNA sequence analyses. Annals of Botany, 103(6):985-997

Garcia-Jacas N, Susanna A, Moxaffarian V, Ilarslan R, 2000. The natural delimitation of Centaurea (Asteraceae: Cardueae): ITS sequence analysis of the Centaurea jacea group. Plant Systematics and Evolution, 223:185-199

Garcia-Jacas N, Susanna A, Vilatersana R, Guara M, 1998. New chromosome counts in the subtribe Centaureinae (Asteraceae, Cardueae) from west Asia, II. Botany Journal of the Linnaean Society, 128:403-412

Garcia-Jacas N, Uysal T, Romashchenko K, Suarez-Santiago VN, Erturul K, Susanna A, 2006. Centaurea revisited: a molecular survey of the Jacea group. Annals of Botany, 98(4):741-753

Hosoki T, Kimura D, 1997. Micropropagation of Centaurea macrocephala Puschk. ex Willd. by shoot-axis splitting. HortScience, 32(6):1124-1125

Keil DJ, Ochsmann J, 2006. Centaurea. In: Flora of North America north of Mexico [ed. by Flora of North America] Oxford, UK: Oxford University Press, 181-194

Klokov MB, Sonsovskii DI, Tsvelev NN, Cherepanov CK, 1963. Centaurea. In: Flora of the USSR, Volume XXVIII: Compositae, tribes Cynareae and Mutisieae [ed. by Bobrov EG, Czerepanov SK], 370-579

Kurtto A, Lahti T, 1987. Checklist of the vascular plants of Finland. (Suomen putkilokasvien luettelo) Pamphlet of the Botanical Museum, University of Helsinki, 11:1-163

Peachey E, 2009. Pacific Northwest Weed Management Handbook. Corvallis, USA: Oregon State University.

Preston CD Pearman DA Dines TD, 2002. New Atlas of the British and Irish Flora. An Atlas of the Vascular Plants of Britain, Ireland, the Isle of Man and the Channel Islands. Oxford, UK: Oxford University Press, 928 pp

Prodan I, 1930. [English title not available]. (Centaureele Romaniei) Buletinul Academieide Cluj Institulul de Arte Grafice. "Ardealul" Strada, Memorandului., 256 pp

Pyšek P, Sadlo J, Mandak B, 2002. Catalogue of Alien Plants of the Czech Republic. Preslia, Praha, 74:97-186

Reynaud J, Couble A, Raynaud J, 1992. Flavonoids from Centaurea macrocephala Muss Pusch. Ex Willd (Compositae). Pharmazie, 47:51-52

Ribeiro NL, Nahar L, Kurmarasamy Y, Mir-Babayev N, Sarker SD, 2002. Flavonoid C-glucosides and a lignan from Centaurea macrocephala (Compositae). Biochemical Systematics and Ecology, 30(11):1097-1100

Rice P, 2009. Invaders Database System. Montana, USA: University of Montana-Missoula.

Roché CT, 1991. Bighead Knapweed (Centaurea macrocephala Puschk.). PNW Extension Bulletin, 386:2 pp

Roché Jr BF, Piper GL, Talbott CJ, 1986. Knapweeds of Washington, EB1393. Washington, USA: Washington State University, 41 pp

Roché Jr BF, Talbott CT, 1986. The Collection History of Centaureas Found in Washington State, XB0978. Research Bulletin Washington State University:36 pp

Shoeb M, Rahman MM, Nahar L, Delazar A, Jaspars M, Macmanus SM, Sarker SD, 2004. Bioactive lignans from the seeds of Centaurea macrocephala. DARU, 12(3):87-93

Susanna A, Garcia-Jacas N, Soltis DE, Soltis PS, 1995. Phylogenetic relationships in the tribe Cardueae (Asteraceae) based on ITS sequences. American Journal of Botany, 32(8):1056-1068

Thompson K, Jalili A, Hodgson JG, Hamzeh'ee B, Asri Y, Shirvany S, Yazdani S, Khoshnevis M, Zarrinkamar F, Safavi MA, 2001. Seed size, shape and persistence in the soil in an Iranian flora. Seed Science Research, 11:345-355

Tonian TR, 1980. Relation between chromosome number and some morphological features of Centaureinae Less representatives. Review of Biology, 33(5):552-554

USDA-ARS, 2008. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory.

USDA-NRCS, 2008. The PLANTS Database. Baton Rouge, USA: National Plant Data Center.

USDA-NRCS, 2011. The PLANTS Database. Baton Rouge, USA: National Plant Data Center.

Wagenitz G, 1975. Centaurea. In: Flora of Turkey and the East Aegean Islands, volume 5 [ed. by Davis PH] Edinburgh, UK: Edinburgh University Press, 522

Washington State Legislature, 1997. Revised Code of Washington, Chapter 17.10: Dispositions Noxious Weeds - control boards. Washington, USA: Washington State Legislature.

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WSDA Plant Protection Division, 2008. Plants and seeds whose sales are prohibited in Washington State. Washington, USA: Washington State Department of Agriculture Plant Protection Division.

WTU, 2009. The University of Washington Herbarium.


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03/08/09 Original text by:

Cindy Roché, Consultant, USA

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