Centaurea calcitrapa L.

purple knapweed

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New England Distribution

Adapted from BONAP data

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North America Distribution

Adapted from BONAP data

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Facts About

Purple knapweed is native to southern Europe and northern Africa. It is an important weed in western North America, but rarely encountered in New England. It can form dense stands and is defended by the vicious spines on the mature involucres.

Habitat

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

Characteristics

Habitat
terrestrial
New England state
Massachusetts
Leaf type
leaves are simple (i.e., lobed or unlobed but not separated into leaflets)
Leaf arrangement
  • alternate: there is one leaf per node along the stem
  • basal: the leaves are growing only at the base of the plant
Leaf blade edges
  • the edge of the leaf blade has lobes, or it has both teeth and lobes
  • the edge of the leaf blade has no teeth or 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
  • NA
  • at least a part of the plume is made up of fine bristles
Spines on plant
  • the plant has no spines
  • there are spines on the plant
Leaf blade length
Up to 200 mm
Disk flower number
21-50
Show All Characteristics
  • Flowers
    Bases of bract appendages
    the bases of two bract appendages are connected by a straight line; there is no projecting edge running between appendages
    Bract color
    the bracts are not colored or tinged with pink, red or purple
    Bract cycle number
    there are three or more cycles of bracts
    Bract margins
    there are fine hairs along the bract margins
    Bract shape
    the main bracts are ovate (egg-shaped)
    Bract spines
    • there is just one simple spine at the tip of the bract
    • there is one spine with branches, at the tip of the bract
    Bract texture
    the bracts appear leathery or hardened
    Bract tip color
    the tips are the same color as the center of the bract
    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
    • the tips of the bracts curve outwards and downwards from the plant
    Bract tip shape
    • NA
    • the tips of the bracts are truncate (end abruptly in a more or less straight line as though cut off)
    Bracts
    there are at least two distinct forms of bracts in different cycles
    Disk flower color
    • blue to purple
    • pink to red
    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, each flower has a single enlarged lobe or strap
    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
    NA
    Flower type in flower heads
    the flower head has disk flowers only, and lacks the strap-shaped flowers
    Height of flower head base
    15–20 mm
    Inflorescence branching (Solidago)
    NA
    Inflorescence shape
    • NA
    • the inflorescence is flat-topped in profile
    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 is compressed (flattened)
    Ovary hair type
    the ovary has no hairs on it
    Ovary hairs
    the ovary has no hairs on it
    Ovary lines or ribs
    there are no lines or ribs visible on the ovary
    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)
    Peduncle length
    At least 0 mm
    Ray flower color
    NA
    Ray flower reproductive parts
    NA
    Ray flowers
    0
    Reproductive system
    all the flowers on the plant contain both carpels and stamens
    Scale tip
    NA
    Smaller bracts at base of bracts
    there is no smaller, outer cycle of bracts
    Style branch number
    the style has two branches
    Width of flower head base
    7–15 mm
  • Fruits or seeds
    Number of pappus parts
    0
    Ovary length in developed fruit
    2.5–3.4 mm
    Seed hair tuft details
    • NA
    • the pappus hairs are hooked or barbed
    Seed hair tuft length
    At least 0 mm
    Seed tuft type
    • the pappus is made of very fine hairs or bristles
    • there is no pappus on the ovary
    Top of disk flower ovary
    NA
    Tuft or plume on fruit
    • NA
    • at least a part of the plume is made up of fine bristles
  • 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 annual, it lacks evidence of previous years' growth
    • the plant is biennial, it appears as either first year (non-reproductive) plants or second year plants with flowers or fruit
    • the plant is perennial, it shows evidence of previous year's leaves, stems or stem bases
    Spines on plant
    • the plant has no spines
    • there are spines 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
    • the upper side of the leaf is not hairy, or has very few hairs
    Leaf arrangement
    • alternate: there is one leaf per node along the stem
    • basal: the leaves are growing only at the base of the plant
    Leaf blade base
    • the leaf has a distinct petiole
    • the leaf has no 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 edges
    • the edge of the leaf blade has lobes, or it has both teeth and lobes
    • the edge of the leaf blade has no teeth or lobes
    Leaf blade hairs
    • NA
    • the leaf blade has tangled or woolly-looking hairs
    Leaf blade length
    Up to 200 mm
    Leaf blade shape
    • the leaf blade is linear (very narrow with more or less parallel sides)
    • 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 tip
    • the tip of the leaf blade is acuminate (tapers to a long, thin point)
    • 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
    • the lower leaves are larger, toothier, and/or on longer stalks than the upper leaves
    Leaf spines
    there are no spines on the leaf edges
    Leaf stalk
    • the leaves have leaf stalks
    • the leaves have no leaf stalks, but attach directly to the stem
    Leaf tip extension
    NA
    Leaf type
    leaves are simple (i.e., 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 leaf has a row of two or more lobes on each side of the central axis, and each lobe itself has rows of lobes on each side of the lobe's central axis
    • the leaf has lobes that themselves have lobes, and these secondary lobes also have lobes; there may be more than three levels of lobes
  • Place
    Habitat
    terrestrial
    New England state
    Massachusetts
    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 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

Wetland Status

Not classified

New England Distribution and Conservation Status

Distribution

Connecticut
absent
Maine
absent
Massachusetts
present
New Hampshire
absent
Rhode Island
absent
Vermont
absent

Conservation Status

None

Native to North America?

No

Sometimes Confused With

Centaurea diffusa:
apical spine of involucral bracts mostly 2-3 mm long and involucre 5-5 mm wide (vs. C. calcitrapa, with the apical spine of involcural bracts mostly 5-25 mm long and involucre mostly 7-12 mm wide).

Synonyms

  • Centaurea adulterina Morreti

Family

Asteraceae

Genus

Centaurea

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Information from Dichotomous Key of Flora Novae Angliae

2.  Centaurea calcitrapa L. E

purple knapweed. Centaurea adulterina Morreti • MA. Roadsides, fields, waste areas.