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Montana Field Guides

Black Starthistle - Centaurea nigra
Other Names:  Black Knapweed, Lesser Knapweed, Centaurea pratensis [illegitimate name], Centaurea jacea ssp. nigra, Centaurea nemoralis

Non-native Species

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

Agency Status
MNPS Threat Rank:
C-value: 0

External Links

State Rank Reason (see State Rank above)
Centaurea nigra is a plant native to Eurasia and introduced worldwide (FNA 2006). A conservation status rank is not applicable (SNA) because the plant is an exotic (non-native) 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. 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 or elliptic, 5–25 cm long blades. Leaf margins are entire to shallowly dentate to irregularly pinnately lobed. Upper stem leaves become gradually smaller, are linear to lanceolate with entire or dentate margins. Source: FNA 2006.

INFLORESCENCE: Corymbiform. Few flower heads are borne on leafy-bracted stems. Flowering heads are composed of disk florets and purple (rarely white) petals. Involucres appear totally black, are ovoid to campanulate or hemispheric, and 15–18 mm high (usually about as wide as high). Involucral bracts are dark brown to black and any green portions are mostly covered by the black fringe of adjacent bracts. Inovlucral bracts are more-or-less triangular with margins evenly fringed (fimbriate) into numerous wiry lobes, but not spine-tipped. The body of the bract is tomentose or glabrous and usually concealed by the expanded fringe from adjacent bracts. Source: FNA 2006.

Flowering June to October (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
Introduced to western and northeastern U.S. and adjacent Canada (Lesica et al. 2012). Native to Eurasia (FNA 2006).

Observations in Montana Natural Heritage Program Database
Number of Observations: 11

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



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

Roadsides, fields, clearings, and waste areas at elevations from 0 to 300 meters (FNA 2006).

Reproductive Characteristics
See also Diagnostic Characteristics.

Flowering heads are composed of about 40 to 100, purple (rarely white) ray florettes (FNA 2006). All florets are fertile florets corollas from 15-18 mm long. The fruit (cypselae) is tan, 2.5-3.0 mm long and finely hairy. The pappus is made of blackish bristles, 0.5-1 mm long, that easily detach.

  • Literature Cited AboveLegend:   View Online Publication
    • 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.
    • Lesica, P., M. T. Lavin, and P. F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
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Citation for data on this website:
Black Starthistle — Centaurea nigra.  Montana Field Guide.  .  Retrieved on , from