Brown Starthistle - Centaurea jacea
Brown Knapweed, Brownray Knapweed,
Centaurea pratensis [illegitimate name], Jacea pratensis
* (see State Rank Reason below)
MNPS Threat Rank
State Rank Reason (see State Rank above)
Centaurea jacea 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.
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Brown Starthistle (Centaurea jacea) Conservation Status Review
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PLANTS: A herbaceous perennial with erect, simple or branched stems that grow to heights of 20–80 cm (FNA 2006; Lesica et al. 2012). Plants are hispid to puberulent (Lesica et al. 2012).
LEAVES: Basal and lower stem leaves are long-petiolate with oblanceolate, 4–15 cm long, blades (Lesica et al. 2012). Leaf margins are entire to shallowly dentate to pinnately lobed (FNA 2006).
INFLORESCENCE: Corymbiform with few purple (rarely white) flowering heads. Involucres 15-18 mm tall. Lower portion of the involucral bracts (bodies) have entire margins and their upper portions have fringed appendages that are little to not decurrent along the margin. Involucral bracts are light to dark brown, roundish (seldom triangular), but not spine-tipped, scarious, and more-or-less undivided to irregularly lacerate. Florets are disc flowers that have no pappus.
Flowering June to October (FNA 2006).
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.
Introduced in western and northeast U.S. and Canada (Lesica et al. 2012). Native to Eurasia (FNA 2006).
Observations in Montana Natural Heritage Program Database
Number of Observations:
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(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).
Flowering heads are composed of 40 to 100, purple (rarely white) disk flowers (FNA 2006). The outer florets are sterile, enlarged, and exceed the fertile inner florets. The inner florets have corollas of 15–18 mm long (FNA 2006, Lesica et al. 2012). The pappus is absent. Achenes are 2–3 mm long.
- 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.