Weed Information: Centaurea nigra (knapweed, black)
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Centaurea nigra (knapweed, black)

Family: Asteraceae

Description

One of the parents of meadow knapweed, the bracts very black with long pectinate segments. Similar to spotted knapweed but with larger heads and entire leaves.

Characteristics

Flower Color
  • Blue-purple
  • Purple
  • Red-purple
Inflorescence Type (How the flowers are arranged on the plant)
  • Corymb
  • Cyme (simple or branched)
  • Head
  • Panicle
Number of Petals
  • 5 petals
  • more than 10 petals
Petal Separation
  • Completely free to base
  • United > 75% of length
Petal Tip
  • Pointed
Flower Symmetry
  • Flowers regular
Flower Length (Head length in the Asteraceae)
  • 1.0 cm (.40 inch)
  • 1.5 cm (.6 inch)
  • 2.0 cm (.8 inch)
  • 2.5 cm (1.0 inch)
Flower Width (Head width in the Asteraceae)
  • 2.0 cm (.80 inch)
  • 2.5 cm (1.0 inch)
  • 3.0 cm (1.2 inches)
  • 3.5 cm (1.4 inches)
  • 4.0 cm (1.6 inches)
  • 4.5 cm (1.8 inches)
  • 5.0 cm (2.0 inches)
Number of Sepals
  • sepals lacking
  • more than 10 sepals
Sepal Separation
  • Completely free to base
Sepal Tip
  • Laciniate
  • Pointed
Flower Sex
  • Bisexual (perfect)
Number of Styles
  • 1 style
Number of Stamens
  • 5 stamens
Stamens Attached to the Petals
  • Stamens attached to the petals
Stamens Connate (united)
  • Anthers united, syngynoecious

Carpel Separation
  • Carpels united (or one)
Number of Carpels
  • 1 carpel
Ovary Position
  • Inferior (epigynous)
Fruit Type
  • Achene
Fruit Length at Maturity
  • 2 mm (.08 inch)
  • 3 mm (.12 inch)
  • 4 mm (.16 inch)
Fruit Width at Maturity
  • 1 mm (.04 inch) or less
  • 2 mm (.08 inch)
Burs
  • Fruit or seed NOT bur-like

Leaf Arrangement
  • Alternate
Leaf Type
  • Simple (including lobed leaves)
Stipules
  • Lacking
Tendrils
  • Tendrils absent
Venation
  • Pinnate
Petiole (leaf stem) Blade Ratio
  • Petiole absent (leaf sessile)
  • Petiole < 25% total length
  • Petiole 25% - 75% total length
Leaf Length (blade PLUS petiole)
  • 2 - 4 cm (.80 - 1.60 inches)
  • 4 - 10 cm (1.60 - 4.0 inches)
  • 1 - 2 dm (4.0 - 8.0 inches)
Leaf Width
  • 1 - 2 cm (.40 - .80 inch)
  • 2 - 4 cm (.80 - 1.6 inches)
Leaf Shape (simple leaves only)
  • Elliptic
  • Lanceolate
  • Pinnately lobed
Leaf or Leaflet Margin
  • Dentate
  • Entire
  • Lobed
Leaf or Leaflet Blade Base
  • Acute (cuneate)
Leaf or Leaflet Tip
  • Acute
  • Rounded (obtuse)
Leaf or Leaflet Blade Surface
  • Scabrous (like sand paper)
Succulence
  • Not succulent

Milky Juice
  • Juice NOT milky (watery)
Woodiness
  • Herbaceous
Spines or Thorns
  • Spines or Thorns ABSENT
Aromatic (vegetative structures)
  • Not aromatic
Life Cycle
  • Perennial
Growth Habit (while flowering)
  • Erect, columnar (narrow)
  • Erect, spherical (bushy)
Plant Height at Maturity
  • 4 - 6 dm (1.3 - 2.0 feet)
  • 6 - 8 dm (2.0 - 2.6 feet)
  • 8 - 10 dm (2.6 - 3.3 feet)
  • 1 - 1.5 meters (3.3 - 5.0 feet)
Wind Dissemination
  • Not wind disseminated
Moisture Regime
  • Seasonally saturated
  • Mesic
Chlorophyll
  • Present

Stem Cross Section
  • Round
Flowering Stem Leaves
  • Stem uniformly leafy
Main Stem Branches
  • Main stem branched

Root or Vegetative Propagule
  • Rhizomatous
  • Tap Root

US State
  • Connecticut
  • Delaware
  • Illinois
  • Kentucky
  • Massachusetts
  • Maine
  • Michigan
  • Missouri
  • North Carolina
  • New Hampshire
  • New Jersey
  • New York
  • Ohio
  • Pennsylvania
  • Virginia
  • Wisconsin
  • West Virginia
  • Indiana
  • Maryland
  • Rhode Island
  • Vermont
  • California
  • Iowa
  • Idaho
  • Minnesota
  • Montana
  • Oregon
  • Washington
Canadian Province or Territory
  • British Columbia
  • New Brunswick
  • Nova Scotia
  • Ontario
  • Prince Edward Island
  • Quebec
  • Newfoundland
Other
  • District of Columbia
  • St. Pierre and Miquelon

  • Common Weeds of Canada, Mulligan 1987 (ISBN 0-910053-59-9) See page: 106
  • Gilkey`s Weeds of the Pacific Northwest, 1980 (ISBN 0-88246-039-0) See page: 331
  • Ontario Weeds, 1992 Agdex 640, Publication #505 See page: 244
  • Weeds of California and other Western States, 2007 (ISBN 13: 978-1-879906-69-3) See Page: 243
  • Weeds of Canada, 1970 Canada Dept. of Ag., Pub. # 948, See page: 193
  • Weeds of the Northeast, 1956, Univ. of Delaware Field Manual #1 See species #: 307
  • Weeds of the Northern United States and Canada, 1964 Montgomery See page: 177
  • Listed as a `Weed` by the Biota of North America Program, 2008 X
  • Listed in the WSSA Composite List of Weeds X
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