Cirsium muticum Michx.

swamp thistle

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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

Swamp thistle is a native thistle of wetland margins and saltmarsh margins. The swamp metalmark butterfly lays its eggs on this species, and the catepillar dines exclusively on it.

Habitat

Brackish or salt marshes and flats, marshes, shores of rivers or lakes, wetland margins (edges of wetlands)

Characteristics

Habitat
  • terrestrial
  • wetlands
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island
  • Vermont
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
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
Spines on plant
there are spines on the plant
Leaf blade length
150–550 mm
Show All Characteristics
  • Flowers
    Bases of bract appendages
    NA
    Bract cycle number
    there are three or more cycles of bracts
    Bract inner side hairs
    the bracts are hairy on their inner surfaces
    Bract outer side hair type
    the bracts are hairy, with simple hairs on their outer surface
    Bract outer side hairs
    the bracts are hairy on their outer surfaces
    Bract shape
    • the main bracts are lanceolate (widest above the base, then taper narrowly towards the tip)
    • the main bracts are linear (long and very narrow)
    Bract spines
    • the bracts have no spines
    • there is just one simple spine at the tip of the bract
    Bract tip extension appearance
    NA
    Bract tip extension edge
    there are no projections from the bract 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
    • white
    Disk flower lobe number
    5
    Disk flower proportions
    • 31-45%
    • 46-75%
    Disk flower reproductive parts
    the disk flower has both pollen- and seed-producing parts
    Disk flower shape
    the disk flower is abruptly widened at some point below the lobes
    Flower head number
    • each flowering stem has four or more flower heads on it
    • 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, and are of similar size as those in the center of the disk
    Flower head platform
    the base has fine, short hairs on it
    Flower head platform surface
    NA
    Flower head shape
    the sides of the flower head are roughly parallel, like a cylinder
    Flower type in flower heads
    the flower head has disk flowers only, and lacks the strap-shaped flowers
    Height of flower head base
    20–50 mm
    Inflorescence branching (Solidago)
    NA
    Inflorescence shape
    • the inflorescence is flat-topped in profile
    • the inflorescence is not flat-topped but appears rounded, with some flower heads distinctly higher than others
    Ovary attachment
    the ovary is attached at or near the base
    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 egg-shaped, but widest above the middle
    Ovary surface
    the ovary surface has no points, bumps or wrinkles, though it may have lines, ribs or wings
    Peduncle length
    0–150 mm
    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
    Rim at top of ovary
    the central flowers have a disk-shaped platform above the ovary
    Scale tip
    NA
    Smaller bracts at base of bracts
    there is no smaller, outer cycle of bracts
    Width of flower head base
    10–30 mm
  • Fruits or seeds
    Number of pappus parts
    11 or more
    Ovary length in developed fruit
    4.5–5.5 mm
    Seed hair tuft bases
    the pappus hairs are attached to one another near the base
    Seed hair tuft details
    the pappus hairs have smaller hairs along their sides
    Seed hair tuft length
    12–20 mm
    Seed hairs uniform
    all the pappus hairs are approximately the same length
    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
  • Glands or sap
    Bract resin
    the bracts have resin or resin glands
    Leaf blade glands
    the leaf blades have no 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 biennial, it appears as either first year (non-reproductive) plants or second year plants with flowers or fruit
    Spines on plant
    there are spines on the plant
    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
    Leaf arrangement
    alternate: there is one leaf per node along the stem
    Leaf blade base
    • the leaf has a distinct petiole
    • the leaf has no petiole
    • the leaf has no petiole and at the base it clasps the stem, or goes all the way around the stem so the stem appears to pierce the leaf
    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
    • there is a noticeable powdery or waxy bloom on the underside of the leaf
    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
    150–550 mm
    Leaf blade shape
    • the leaf blade is elliptic (widest near the middle and tapering at both ends)
    • the leaf blade is obovate (egg-shaped, but with the widest point above the middle of the leaf blade)
    • 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 veins
    the leaf blade has one main vein running from the base towards the tip
    Leaf blade width
    40–200 mm
    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 spines along the leaf edges
    Leaf stalk
    • the leaves have leaf stalks
    • the leaves have no leaf stalks, but attach directly to the stem
    Leaf stalk length
    At least 0 mm
    Leaf tip extension
    NA
    Leaf type
    leaves are simple (i.e., lobed or unlobed but not separated into leaflets)
    Leaflet number
    0
    Specific leaf type
    the leaf has a row of two or more lobes on each side of the central axis
  • Place
    Habitat
    • terrestrial
    • wetlands
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • New Hampshire
    • Rhode Island
    • Vermont
    Specific habitat
    • brackish or salt marshes and flats
    • edges of wetlands
    • marshes
    • shores of rivers or lakes
  • Scent
    Plant odor
    the plant does not have much of an odor
  • 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 length
    At least 0 mm
    Stem internode hair type
    • at least some of the hairs on the stem are tangled, matted or woolly
    • the stem has no hairs between the nodes
    Stem internode hairs
    • the stem has hairs between the nodes
    • the stem has no hairs between the nodes
    Stem wings
    the stem does not have wings on it

Wetland Status

Occurs only in wetlands. (Wetland indicator code: OBL)

New England Distribution and Conservation Status

Distribution

Connecticut
present
Maine
present
Massachusetts
present
New Hampshire
present
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)
Vermont
uncommon (S-rank: S3)

Native to North America?

Yes

Sometimes Confused With

Cirsium pumilum:
outer involucral bracts tipped by a prominent spine 3-6 mm long (vs. C. muticum, with the outer involucral bracts lacking a spine at apex or tipped by a short one up to 1 mm long).

Synonyms

  • Carduus muticus (Michx.) Pers.
  • Cirsium bigelovii DC.
  • Cirsium muticum var. monticola Fern.
  • Cirsium muticum var. subpinnatifidum (Britt.) Fern.

Family

Asteraceae

Genus

Cirsium

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Information from Dichotomous Key of Flora Novae Angliae

6.  Cirsium muticum Michx. N

swamp thistle. Carduus muticus (Michx.) Pers.; Cirsium bigelovii DC.; C. muticum Michx. var. monticola Fern.; C. muticum Michx. var. subpinnatifidum (Britt.) Fern. • CT, MA, ME, NH, RI, VT. 
Wet depressions, margins of wetlands, shorelines, upper edges of saltmarshes.