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Centaurea stoebe — spotted knapweed

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Facts

Spotted knapweed is a serious threat to the rangelands of the western United States. It was probably introduced to North America from Europe as a contaminent in alfalfa seed or in ships' ballast.

Habitat

Anthropogenic (man-made or disturbed habitats), meadows and fields

New England distribution

Adapted from BONAP data

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North America distribution

Adapted from BONAP data

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Characteristics

Habitat
terrestrial
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island
  • Vermont
Leaf type
  • leaves are compound (made up of two or more discrete leaflets)
  • leaves are simple (lobed or unlobed but not separated into leaflets)
Leaf arrangement
alternate: there is one leaf per node along the stem
Leaf blade edges
the edge of the leaf blade has lobes, or it has both teeth and lobes
Flower type in flower heads
the flower head has disk flowers only, and lacks the strap-shaped flowers
Ray flower color
NA
Tuft or plume on fruit
  • at least a part of the plume is made up of fine bristles
  • there is no plume, or the plume is made up of scales, awns, a crown, or a rim
Spines on plant
the plant has no spines
Leaf blade length
100–150 mm
Flower head width
8–13 mm
Disk flower number
21-50
Show all characteristics

  • Flowers

    Bases of bract appendages
    bases of bract appendages are u-shaped, with a tiny projecting edge running across from one appendage to the next
    Bract cycle number
    there are three or more cycles of bracts
    Bract margins
    there are few or no fine hairs along the bract margins
    Bract outer side hair type
    • the bracts are hairy on their outer surfaces, with curled, tangled, matted, or woolly hairs
    • the bracts are not hairy on their outer surface
    Bract outer side hairs
    • the bracts are hairy on their outer surfaces
    • the bracts are not hairy on their outer surfaces
    Bract shape
    the main bracts are oblong (roughly rectangular but rounded at the ends)
    Bract tip extension appearance
    the projections from the bract tips have further projections from their edges, like a fringe
    Bract tip extension edge
    there are projections from the bract tips
    Bract tip orientation
    the bracts are pressed against the plant, or spreading out at the tips
    Bract tip shape
    • the tips of the bracts acute (have a sharp point)
    • the tips of the bracts are obtuse (have a blunt point)
    Disk flower color
    • blue to purple
    • pink to red
    • white
    Disk flower lobe number
    5
    Disk flower number
    21-50
    Disk flower reproductive parts
    the disk flower has both pollen- and seed-producing parts
    Disk flower shape
    the disk flower is tube-shaped (cylindrical), or gradually widening like a funnel
    Flower head number
    each flowering stem has only one to three flower heads on it
    Flower head outer flowers
    at the outer edge of the flower head, the flowers have no enlarged lobe or strap, but are bigger than the flowers in the center of the disk
    Flower head platform
    the base has fine, short hairs on it
    Flower head platform surface
    NA
    Flower head position
    each of the flower heads is separate on its own peduncle (stalk), not clustered in groups
    Flower head profile
    the disk is flat or nearly flat across the top
    Flower head shape
    • the flower head is shaped like a cone with the point up
    • the sides of the flower head are roughly parallel, like a cylinder
    Flower head width
    8–13 mm
    Flower type in flower heads
    the flower head has disk flowers only, and lacks the strap-shaped flowers
    Height of flower head base
    10–13 mm
    Inflorescence branching (Solidago)
    NA
    Inflorescence shape
    NA
    Ovary attachment
    the ovary is attached at the side near the base, rather than at the base
    Ovary beak
    there is no beak on the ovary
    Ovary cross-section
    • the ovary has five or more corners in cross-section
    • the ovary is compressed (flattened)
    Ovary hair type
    the ovary has hairs on it, but the hairs have no glands
    Ovary hairs
    the ovary has hairs on it
    Ovary profile
    • in profile, the ovary is oblong (roughly rectangular but rounded at the ends)
    • in profile, the ovary is roughly elliptical (widest in the middle, tapering to both ends)
    Ray flower color
    NA
    Ray flower reproductive parts
    NA
    Ray flowers
    0
    Ray length
    0 mm
    Reproductive system
    all the flowers on the plant contain both carpels and stamens
    Scale tip
    NA
    Style branch number
    the style has two branches
    Width of flower head base
    6–8 mm

  • Fruits or seeds

    Ovary length in developed fruit
    2–3.5 mm
    Seed hair tuft color
    the pappus hairs are white or off-white
    Seed hair tuft length
    1–3 mm
    Seed tuft scale number
    0
    Seed tuft type
    the pappus is made of very fine hairs or bristles
    Top of disk flower ovary
    NA
    Tuft or plume on fruit
    • at least a part of the plume is made up of fine bristles
    • there is no plume, or the plume is made up of scales, awns, a crown, or a rim

  • Glands or sap

    Leaf blade glands
    the leaf blades have glandular (translucent) dots or scales
    Sap
    the sap is clear and watery

  • Growth form

    Growth form
    the plant has one or more free-standing stems
    Plant lifespan
    the plant is perennial, it shows evidence of previous year's leaves, stems or stem bases
    Spines on plant
    the plant has no spines
    Underground organs
    there is a thickened taproot on the plant

  • Leaves

    Hairs on underside of leaf blade
    • the underside of the leaf is fuzzy or hairy
    • the underside of the leaf is not hairy, or has very few hairs
    Hairs on upper side of leaf blade
    the upper side of the leaf is fuzzy or hairy
    Leaf arrangement
    alternate: there is one leaf per node along the stem
    Leaf blade base
    the leaf has a distinct petiole
    Leaf blade base shape
    the base of the leaf blade is cuneate (wedge-shaped, tapers to the base with relatively straight, converging edges), or narrow
    Leaf blade bloom
    the underside of the leaf has no noticeable bloom
    Leaf blade edges
    the edge of the leaf blade has lobes, or it has both teeth and lobes
    Leaf blade hairs
    the leaf blade has tangled or woolly-looking hairs
    Leaf blade length
    100–150 mm
    Leaf blade shape
    • the leaf blade is lanceolate (lance-shaped; widest below the middle and tapering at both ends)
    • the leaf blade is oblong (rectangular but with rounded ends)
    • the leaf blade is ovate (widest below the middle and broadly tapering at both ends)
    Leaf blade surface colors
    there is no noticeable color variation on the upper surface of the leaf
    Leaf blade tip
    the tip of the leaf blade is acute (sharply pointed)
    Leaf disposition
    the leaves are nearly similar in size, prominence of teeth, and length of stalks throughout the stem
    Leaf spines
    there are no spines on the leaf edges
    Leaf stalk
    the leaves have leaf stalks
    Leaf tip extension
    NA
    Leaf type
    • leaves are compound (made up of two or more discrete leaflets)
    • leaves are simple (lobed or unlobed but not separated into leaflets)
    Specific leaf type
    • the leaf has a row of two or more lobes on each side of the central axis
    • the leaves are simple (lobed or unlobed but not separated into leaflets
    Teeth per side of leaf blade
    At least 0

  • Place

    Habitat
    terrestrial
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • New Hampshire
    • Rhode Island
    • Vermont
    Specific habitat
    • man-made or disturbed habitats
    • meadows or fields

  • Stem, shoot, branch

    Flowering stem cross-section
    the flowering stem is circular, or with lots of small angles
    Leaves on stem
    there is at least one full leaf above the base of the flowering stem
    Stem bloom
    there is no powdery or waxy film on the stem
    Stem internode hair direction
    the hairs point mostly upwards to outwards
    Stem internode hair type
    at least some of the hairs on the stem are tangled, matted or woolly
    Stem internode hairs
    the stem has hairs between the nodes
    Stem wings
    • the stem does not have wings on it
    • the stem has wings on it that run down the stem from the leaf nodes

Wetland status

Not classified

In New England

Distribution

Connecticut
present, invasive, prohibited
Maine
present
Massachusetts
present, invasive, prohibited
New Hampshire
present, invasive, prohibited
Rhode Island
present
Vermont
present

Conservation status

Exact status definitions can vary from state to state. For details, please check with your state.

Massachusetts
unranked (S-rank: SNR)

Subspecies and varieties

Our subspecies is Centaurea stoebe L. ssp. micranthos (Gugler) Hayek.

From Flora Novae Angliae dichotomous key

13. Centaurea stoebe L. ssp. micranthos (Gugler) Hayek E

spotted knapweed. Centaurea biebersteinii DC.; C. maculosa, auct. non Lam.; C. maculosa Lam. ssp. micranthos Gugler • CT, MA, ME, NH, RI, VT. Fields, railroads, open rights-of-way, 
sandy or gravelly banks. This taxon has long been known as Centaurea maculosa Lam.; however, this name properly applies to a strictly biennial knapweed with larger capitula 
(and is included in C. stoebe L. ssp. stoebe).

4×13. Centaurea diffusa × Centaurea stoebe → Centaurea ×‌psammogena Gáyer is a rare knapweed hybrid in New 
England that is frequently confused with C. diffusa. The hybrid, known from MA, 
 is morphologically variable. Involucral bract appendages are usually brown to 
black (rarely light brown), and appendage spines are absent or short (spine mostly 
1 mm long or shorter). However, an evident pappus always crowns the ovary, 
and the marginal flowers of the capitulum are falsely radiant (pappus absent and marginal flowers not enlarged in C. diffusa).

Native to North America?

No

Synonyms

  • Centaurea biebersteinii DC.
  • Centaurea maculosa Lam., misapplied
  • Centaurea maculosa Lam. ssp. micranthos Gugler

Family

Asteraceae

Genus

Centaurea