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Montana Field Guides

Meadow Knapweed - Centaurea x moncktonii
Other Names:  Protean Knapweed, Centaurea debeauxii ssp. Thuillieri, Centaurea jacea var. pratensis, Centaurea jacea ssp. Xpratensis, Centaurea nigra var. radiata, Centaurea thuillieri, Centaurea pratensis (illegitimate)

Non-native Species

Global Rank: GNRTNR
State Rank: SNA
(see State Rank Reason below)

Agency Status
USFWS:
USFS:
BLM:
MNPS Threat Rank:
C-value:

External Links






State Rank Reason (see State Rank above)
Centaurea xmoncktonii is a hybrid plant native to Europe or originated in North America from European ancestry (FNA 2006). A conservation status rank is not applicable (SNA) because the plant is an exotic (non-native) hybrid in Montana that is not a suitable target for conservation activities.
 
General Description
PLANTS: A herbaceous perennial with erect, simple or branched stems that grow to heights of 30-150 cm (FNA 2006). Plants villous to scabrous with septate hairs and loosely tomentose or more or less glabrate. Source: FNA 2006.

LEAVES: Basal and lower stem leaves are petiolate with oblanceolate, 5–25 cm long blades. Leaf margins are entire to shallowly dentate to irregularly pinnately lobed. Upper stem leaves become gradually smaller and are linear to lanceolate with entire or dentate margins. Source: FNA 2006.

INFLORESCENCE: Corymbiform. Few, but relatively broad flowering heads are borne on leafy-bracted stems. Flowering heads are composed of ray (not disk) florets with purple (rarely white) petals. Involucres are ovoid to campanulate or hemispheric and 15–18 mm high (usually about as wide as high). Involucral bracts are light to dark brown, more-or-less triangular, and margins coarsely dentate to evenly fringed (fimbriate), but not spine-tipped. Source: FNA 2006.

Phenology
Flowering May to November (FNA 2006).

Diagnostic Characteristics
The Centaurea jacea complex has been the subject of much controversy (FNA 2006). These plants are widely distributed in Europe and variable in easily noticeable characteristics of their flowering heads, florets, and fruits (cypselae). Within this complex, numerous species have been named, but all are capable of interbreeding, and natural hybridization has resulted in intermediates that variously combine the features of their parents. These intermediates have been considered as species or as infraspecific taxa within the parental species. This has resulted in tangled nomenclature, further complicated by names misapplied in their use and infraspecific names that are inadequately indexed.

For the Centaurea jacea complex, MTNHP follows the Centaurea treatment by Keil & Ochsmann in FNA, Vol. 19 (2006). 3 species (Centaurea jacea, Centaurea nigra, Centaurea nigrescens) and 1 nothospecies [formed by direct hybridization of 2 species and not by other hybrids], Centaurea xmoncktonii are recognized in MT. However, all could be treated as 1 species, Centaurea jacea with 3 subspecies (jacea, nigra, nigrescens) and 1 nothosubspecies hybrid, C. jacea ssp. xpratensis.

The complex of Centaurea jacea, Centaurea nigra, Centaurea nigrescens, Centaurea xmoncktonii share characteristics of: a) Perennial, b) Involucres 15-18 mm tall, c) Lower portion of the involucral bracts have entire margins and their upper portion have fringed appendages that are little to not decurrent along the margin and are not spine-tippped. They are distinguished by the following characteristics.

Centaurea jacea: Involucral bracts are light to dark brown, roundish (seldom triangular), scarious, and more-or-less undivided to irregularly lacerate. Florets are disc flowers that lack a pappus.

Centaurea nigra: Involucres appear totally black and are usually about as wide as high. Involucral bracts are dark brown to black; any green portion is mostly covered by the black fringe of adjacent bracts. Bracts are more-or-less triangular with margins evenly fringed into numerous wiry lobes. The body of the bract is tomentose or glabrous. Florets are disc flowers with a blackish pappus of 0.5-1.0 mm long bristles that easily detach.

Centaurea nigrescens: Involucres are relatively narrow, usually longer than wide. Involucral bracts appear black and green; green portions are mostly not covered by the black fringe of adjacent bracts. Bracts are more-or-less triangular with irregularly dentate or lobed margins. Florets have no pappus or have many bristles of unequal length that easily detach.

Centaurea xmoncktonii: Involucres are relatively broad. Involucral bracts are light to dark brown, more-or-less triangular, and have variable margins from coarsely dentate to evenly fringed. Sterile florets are somewhat expanded and exceed the length of the 15-18 mm long fertile florets. Florets are of ray flowers and have none or 0.5-1.0 mm long pappus bristles that easily detach.

Range Comments
Native to Europe or originated in North America from European ancestry (FNA 2006). Observations from northwest Montana have been reported and specimens are needed for Montana’s herbaria.

Observations in Montana Natural Heritage Program Database
Number of Observations: 13

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density

Recency

 

(Observations spanning multiple months or years are excluded from time charts)



Habitat
Roadsides, riverbanks, pastures, meadows, forest openings, and waste areas at elevations from 0 to 1,000 meters (FNA 2006).

Ecology
POLLINATORS
The following animal species have been reported as pollinators of this species or genera where their geographic ranges overlap: Bombus vagans, Bombus bifarius, Bombus centralis, Bombus fervidus, Bombus rufocinctus, Bombus ternarius, Bombus terricola, Bombus occidentalis, Bombus griseocollis, Bombus impatiens, Bombus insularis, and Bombus suckleyi (Thorp et al. 1983, Johnson 1986, Colla and Dumesh 2010, Koch et al. 2012, Williams et al. 2014, Tripoldi and Szalanski 2015).

Reproductive Characteristics
Flowering heads are composed of about 40 to 100, purple (rarely white) ray florets (FNA 2006). Sterile florets are somewhat expanded and exceed the length of the 15-18 mm long fertile florets. The fruit (cypselae) is tan, 2.5-3.0 mm long and finely hairy. The pappus is absent or there are 0.5-1.0 mm long bristles that easily detach.

Management
Meadow knapweeds represent an array of mutually interfertile intermediates derived by hybridization and backcrossing among the various diploid and tetraploid individuals that make up the Centaurea jacea complex (FNA 2006). The plants variously combine features of Centaurea jacea and Centaurea nigra and possibly Centaurea nigrescens (FNA 2006). Meadow knapweeds are often found without either parent in the immediate vicinity (FNA 2006).

Meadow knapweeds appear to respond to herbicides differently from their other Centaurea relatives (personal communication from a weed coodinator).

References
  • Literature Cited AboveLegend:   View Online Publication
    • Colla, S.R. and S. Dumesh. 2010. The bumble bees of southern Ontario: notes on natural history and distribution. Journal of the Entomological Society of Ontario 141: 39-68.
    • Flora of North America Editorial Committee. 2006. Flora of North America North of Mexico. Vol. 19. Magnoliophyta: Asteridae, part 6: Asteraceae, part 1. Oxford Univ. Press, New York. xxiv + 579 pp.
    • Johnson, R.A. 1986. Intraspecific resource partitioning in the bumble bees Bombus ternarius and B. pennsylvanicus. Ecology 67:133-138.
    • Koch, J., J. Strange, and P. Williams. 2012. Bumble bees of the western United States. Washington, DC: USDA Forest Service, Pollinator Partnership. 143 p.
    • Thorp, R.W., D.S. Horning, and L.L. Dunning. 1983. Bumble bees and cuckoo bumble bees of California (Hymenoptera: Apidae). Bulletin of the California Insect Survey 23:1-79.
    • Tripoldi, A.D. and A.L. Szalanski. 2015. The bumble bees (Hymenoptera: Apidae: Bombus) of Arkansas, fifty years later. Journal of Melittology 50: doi: http://dx.doi.org/10.17161/jom.v0i50.4834
    • Williams, P., R. Thorp, L. Richardson, and S. Colla. 2014. Bumble Bees of North America. Princeton, NJ. Princeton University Press.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Flora of North America Editorial Committee. 2006. Flora of North America North of Mexico. Vol. 20. Magnoliophyta: Asteridae, part 7: Asteraceae, part 2. Oxford Univ. Press, New York. xxii + 666 pp.
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Citation for data on this website:
Meadow Knapweed — Centaurea x moncktonii.  Montana Field Guide.  .  Retrieved on , from