Weed Information: Knautia arvensis (bluebuttons)
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Knautia arvensis (bluebuttons)

Family: Dipsacaceae

Description

An escaped ornamental perennial which is very invasive in pastures and rangeland. The lower leaves simple, the upper leaves pinnately lobed to parted. The flowers in terminal heads.

Characteristics

Flower Color
  • Red (or pink)
  • Blue
  • Blue-purple
  • Purple
  • Red-purple
Inflorescence Type (How the flowers are arranged on the plant)
  • Head
Number of Petals
  • 4 petals
  • 5 petals
Petal Separation
  • United > 75% of length
Petal Tip
  • Rounded
Flower Symmetry
  • Flowers regular
  • Flowers slightly irregular
Flower Length (Head length in the Asteraceae)
  • 8 mm (.32 inch)
  • 9 mm (.36 inch)
  • 1.0 cm (.40 inch)
  • 1.5 cm (.6 inch)
  • 2.0 cm (.8 inch)
Flower Width (Head width in the Asteraceae)
  • 3 mm (.12 inch)
  • 4 mm (.16 inch)
  • 5 mm (.20 inch)
Number of Sepals
  • 8 sepals
  • 9 sepals
  • 10 sepals
Sepal Separation
  • United at base < 25% length
  • United from 25% - 75% length
  • United > 75% of length
Sepal Tip
  • Pointed
  • Spine-like
Flower Sex
  • Bisexual (perfect)
Number of Styles
  • 1 style
Number of Stamens
  • 4 stamens
Stamens Attached to the Petals
  • Stamens attached to the petals
Stamens Connate (united)
  • Filaments or anthers NOT united

Carpel Separation
  • Carpels united (or one)
Number of Carpels
  • 1 carpel
Ovary Position
  • Inferior (epigynous)
Fruit Type
  • Achene
Fruit Length at Maturity
  • 5 mm (.20 inch)
  • 6 mm (.24 inch)
Fruit Width at Maturity
  • 1 mm (.04 inch) or less
  • 2 mm (.08 inch)
  • 3 mm (.12 inch)
Burs
  • Fruit or seed NOT bur-like

Leaf Arrangement
  • Opposite
Leaf Type
  • Simple (including lobed leaves)
Stipules
  • Lacking
Tendrils
  • Tendrils absent
Venation
  • Pinnate
Petiole (leaf stem) Blade Ratio
  • Petiole < 25% total length
Leaf Length (blade PLUS petiole)
  • 4 - 10 cm (1.60 - 4.0 inches)
  • 1 - 2 dm (4.0 - 8.0 inches)
  • 2 - 4 dm (8.0 - 16.0 inches)
Leaf Width
  • 1 - 2 cm (.40 - .80 inch)
  • 2 - 4 cm (.80 - 1.6 inches)
  • 4 - 10 cm (1.6 - 4.0 inches)
Leaf Shape (simple leaves only)
  • Elliptic
  • Lyrate
  • Pinnately lobed
Leaf or Leaflet Margin
  • Entire
  • Lobed
  • Parted
Leaf or Leaflet Blade Base
  • Acute (cuneate)
  • Acuminate (attenuate)
Leaf or Leaflet Tip
  • Acute
Leaf or Leaflet Blade Surface
  • Hirsute
  • Hispid or setose
  • 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)
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)
Wind Dissemination
  • Not wind disseminated
Moisture Regime
  • Mesic
Chlorophyll
  • Present

Stem Cross Section
  • Ridged
  • Round
Flowering Stem Leaves
  • Stem leaves greatly reduced
  • Stem uniformly leafy
Main Stem Branches
  • Main stem unbranched
  • Main stem branched

Root or Vegetative Propagule
  • Tap Root

US State
  • Connecticut
  • Illinois
  • Massachusetts
  • Maine
  • Michigan
  • New Hampshire
  • New Jersey
  • New York
  • Pennsylvania
  • Wisconsin
  • West Virginia
  • Maryland
  • Vermont
  • Colorado
  • Idaho
  • Minnesota
  • Montana
  • North Dakota
  • Oregon
  • South Dakota
  • Utah
  • Wyoming
Canadian Province or Territory
  • British Columbia
  • New Brunswick
  • Nova Scotia
  • Ontario
  • Quebec
  • Alberta
  • Manitoba
  • Newfoundland
  • Saskatchewan

  • How to Know the Weeds, 1972, (ISBN# 0-697-04880-2) See page: 150
  • Weeds, 1955 (1980) Walter Conrad Muenscher, ISBN# 0-8014-1266-8 See page: 416, 417
  • Weeds of Alberta, 1983 Alberta Environmental Centre Agdex 640-4, See page: 203
  • Weeds of the Northern U.S, and Canada, 1999 Royer and Dickinson, (ISBN# 1-55105-221-0) See page: 282 - 283
  • 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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