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Montana Field Guide

Montana Field Guides

Diffuse Knapweed - Centaurea diffusa
Other Names:  Bushy Star-thistle, White Knapweed

Noxious Weed: Priority 2B
Non-native Species

Global Rank: GNR
State Rank: SNA

Agency Status
USFWS:
USFS:
BLM:
MNPS Threat Rank:
C-value: 0

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General Description
Annual to rarely short-lived perennial. Stems ascending to erect, branched, 30–50 cm. Herbage puberulent to sparsely tomentose, glandular-punctate. Leaves petiolate below, the lowest deciduous; blades oblanceolate, 1–15 cm long, deeply pinnate to bipnnate into linear lobes. Inflorescence paniculate. Involucres ovoid, 10–13 mm high; outer phyllaries ovate, striate, green, tan above, spiny-margined; inner linear-lanceolate. Disk flowers 25 to 35, white, sometimes purple above; the outer slender, inconspicuous; inner corollas 12–13 mm long. Achenes 2–3 mm long; pappus absent or inconspicuous (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Diagnostic Characteristics
This species readily hybridizes with Centaurea stoebe. These fertile hybrids have been named Centaurea x psammogena.

Species Range
Montana Range

Non-native
 


Range Comments
Introduced to most of northern U.S. and adjacent Canada (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 230

(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

Management

References
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Citation for data on this website:
Diffuse Knapweed — Centaurea diffusa.  Montana Field Guide.  .  Retrieved on , from