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• Dichotomous Key
• Asteraceae
• Asteraceae Group 2
• Cirsium
• Cirsium horridulum

Cirsium horridulum — yellow thistle

Facts

A densely hairy and spiny plant, yellow thistle is most commonly found near the coast, including on the upper edges of salt marshes. This plant is protected in several New England states.

Habitat

Brackish or salt marshes and flats, meadows and fields

Characteristics

• Flowers

  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 outer side hair type

  the bracts are hairy on their outer surfaces, with curled, tangled, matted, or woolly hairs

  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

  there is just one simple spine at the tip of the bract

  Bract tip color

  the tips are a different color from the center of the bract

  Bract tip orientation

  the bracts are pressed against the plant, or spreading out at the tips

  Bract tip shape

  • the tips of the bracts are acuminate (tapered to a narrow point)
  • 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
  • white

  Disk flower number

  • 21-50
  • more than 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 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 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
  • the disk is rounded across the top

  Flower head shape

  the flower head is hemispherical (like the bottom half of a sphere)

  Flower head width

  40–80 mm

  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 flower heads grow in clusters from the axils of the branches or leaves
  • the inflorescence is flat-topped in profile

  Inflorescence stem

  • hairs are present on the stem of the inflorescence
  • the stem of the inflorescence is not hairy

  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 roughly egg-shaped

  Peduncle length

  0–50 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

  Scale tip

  NA

  Style branch number

  the style has two branches

  Width of flower head base

  30–80 mm

• Fruits or seeds

  Ovary length in developed fruit

  4–6 mm

  Seed hair tuft details

  the pappus hairs have smaller hairs along their sides

  Seed hair tuft length

  25–35 mm

  Seed hairs uniform

  all the pappus hairs are approximately the same length

  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 no 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
  • the plant is perennial, it shows evidence of previous year's leaves, stems or stem bases

  Spines on plant

  there are spines on the plant

  Underground organs

  • the plant has a rhizome (a horizontal underground stem with roots growing from it)
  • 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
  • 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 teeth

  Leaf blade hairs

  the leaf blade has tangled or woolly-looking hairs

  Leaf blade length

  100–400 mm

  Leaf blade shape

  • the leaf blade is elliptic (widest near the middle and tapering at both ends)
  • the leaf blade is linear (very narrow with more or less parallel sides)
  • the leaf blade is oblanceolate (lance-shaped, but with the widest point above the middle of the leaf blade)
  • the leaf blade is oblong (rectangular but with rounded 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 blade width

  20–100 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 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 leaves are simple (i.e., lobed or unlobed but not separated into leaflets

• Place

  Habitat

  terrestrial

  New England state

  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island

  Specific habitat

  • brackish or salt marshes and flats
  • meadows or fields

• Stem, shoot, branch

  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
  • the stem has no hairs between the nodes

  Stem internode hairs

  the stem has hairs between the nodes

  Stem wings

  the stem does not have wings on it

Wetland status

Usually occurs in non-wetlands, but occasionally in wetlands. (Wetland indicator code: FACU)

New England distribution and conservation status

From the dichotomous key of Flora Novae Angliae