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Spotted Knapweed Centaurea maculosa

Previously known as:

  • Centaurea biebersteinii
  • Centaurea stoebe ssp micranthos
  • Centaurea stoebe ssp stoebe
Phonetic Spelling
sen-TAR-ee-ah mak-yoo-LOH-suh
This plant is an invasive species in North Carolina
Description

Spotted Knapweed is a herbaceous biennial or perennial weed in the Asteraceae family native to Europe and western Asia and is considered invasive in many states within the United States. The plant grows on stream banks, pond shorelines, sand prairies, old fields and pastures, roadsides, and along railroads, and many open, disturbed areas. It crowds out native species and forage for livestock. The species prefers to grow in dry, sterile, gravelly or sandy soils and full sunlight.  

Spotted Knapweed usually has a stout taproot and/or pubescent stems when young. A basal rosette of deeply lobed petiolate leaves covered in fine, short hairs approximately 8 inches in size is produced the first year.  Pubescent stems form when young with highly dissected leaves that are alternate and may be slightly lobed or linear. Leaves become smaller and less lobed toward the top. The stem is erect or ascending, slender, hairy and branching, and can grow up to three feet tall. As many as 6 stems emerge from the same root crown during a single growing season. The flowers are a vibrant lavender with black margins of the flower bract tips which give the flower heads a spotted look, which is the origin of its common name. The fruit is an achene (about a quarter-inch long) finely hairy, straw-colored at maturity with a tuft of short, stiff, light brown bristles at the tip.  The seeds are primarily distributed by the wind. An individual plant may produce as many as 40,000 seeds. 

Light infestations of this invasive weed can be controlled by pulling the weeds by hand or by mowing early when the plant is just beginning to flower. Plants are less likely to regrow if allowed to form flower stalks before mowing. All control methods must be repeated for several years until seeds stored in the soil become depleted. Spotted Knapweed is resistant to some herbicides, likely due to wooly hairs on its stems and leaves limiting retention or penetration of the herbicide.

See this plant in the following landscape:
Cultivars / Varieties:
Tags:
#invasive#weed#weedy#lavender flowers#hairy#dry soils tolerant
 
Cultivars / Varieties:
Tags:
#invasive#weed#weedy#lavender flowers#hairy#dry soils tolerant
  • Attributes:
    Genus:
    Centaurea
    Species:
    maculosa
    Family:
    Asteraceae
    Life Cycle:
    Biennial
    Perennial
    Recommended Propagation Strategy:
    Seed
    Country Or Region Of Origin:
    Europe, Western Asia
    Distribution:
    North Eastern, northern Midwest and western United States
  • Whole Plant Traits:
    Plant Type:
    Weed
    Wildflower
    Habit/Form:
    Erect
    Growth Rate:
    Medium
    Maintenance:
    High
  • Cultural Conditions:
    Light:
    Full sun (6 or more hours of direct sunlight a day)
    Soil Texture:
    Sand
    Shallow Rocky
    Soil pH:
    Acid (<6.0)
    Neutral (6.0-8.0)
    Soil Drainage:
    Occasionally Dry
    Very Dry
    USDA Plant Hardiness Zone:
    5b, 6b, 6a, 7b, 7a, 8a, 8b, 9a, 9b
  • Fruit:
    Fruit Color:
    Black
    Gold/Yellow
    Display/Harvest Time:
    Fall
    Fruit Type:
    Achene
    Fruit Length:
    < 1 inch
    Fruit Width:
    < 1 inch
    Fruit Description:
    An achene (about a quarter-inch long) finely hairy, straw-colored at maturity with a tuft of short, stiff, light brown bristles at the tip.
  • Flowers:
    Flower Color:
    Purple/Lavender
    Flower Inflorescence:
    Cyme
    Head
    Flower Bloom Time:
    Summer
    Flower Shape:
    Dome
    Flower Petals:
    Bracts
    more than 20 petals/rays
    Flower Size:
    1-3 inches
    Flower Description:
    Up to 1 in. lavender flower heads with a harsh, prickly, black-tipped bract
  • Leaves:
    Leaf Color:
    Gray/Silver
    Green
    Leaf Feel:
    Smooth
    Leaf Type:
    Compound (Pinnately , Bipinnately, Palmately)
    Leaf Arrangement:
    Alternate
    Rosulate
    Leaf Shape:
    Linear
    Leaf Margin:
    Lobed
    Hairs Present:
    Yes
    Leaf Length:
    > 6 inches
    Leaf Description:
    A basal rosette of deeply lobed petiolate leaves approximately 8 inches in size is produced the first year. Pubescent stems form when young with highly dissected leaves that are alternate and may be slightly lobed or linear. Leaves become smaller and less lobed toward the apex.
  • Stem:
    Stem Color:
    Gray/Silver
    Green
    Stem Is Aromatic:
    No
    Stem Form:
    Straight
    Stem Surface:
    Hairy (pubescent)
    Stem Description:
    The stem is erect or ascending, slender, hairy and branching, and can grow up to three feet tall. As many as 6 stems emerge from the same root crown during a single growing season.
  • Landscape:
    Landscape Location:
    Meadow
    Naturalized Area
    Problems:
    Invasive Species
    Weedy