This invasive plant took no oath of allegiance before it became naturalized in our meadows, roadsides, overgrazed pastures, and disturbed areas. With head-high branching, winged stems without spines, and leaves armed with ridged spines, these prickly pests form dense stands that defy eradication. NM and many states classify them as noxious weeds. Note the flower head with rows of broad spiny, purple phyllaries under the dense cluster of pink, tassel-like disk flowers, and hairless leaf surfaces.

FLOWERS: June–September. Pink to purple, 2–3-inches diameter (5-7.5 cm), spherical heads usually nodding, pom-pom disk flowers on a head with rows of thorny phyllaries, purple-tinged, broad, lance-shaped with tapering tips.

LEAVES: A basal rosette up to 2-feet in diameter overwinters, then sprouts a branching stem up to 6-feet tall. Stem leaves alternate, deeply lobed, 3–6-inches long (7.5-15 cm), hairless and lined with silvery, thorn-like spines up to 1/2-inch long (1 cm). The leaf base grows downward (decumbent) along the stem creating a winged stem.

HABITAT: Invades pastures, roadsides, disturbed areas; desert scrub, pinyon-juniper, ponderosa-Douglas-fir forests.

ELEVATION: 4,500–8,500 feet.

RANGE: Widespread nationwide.

SIMILAR SPECIES: NM has 12 species of native thistles, Cirsium, and two introduced. The hairless leaves, white spines,winged stems, and round, purple, nodding flower head characterize Carduus nutans. The rare Sacramento Mountain Thistle, Cirsium vinaceum, also has nodding, purple flower heads but not winged stems.

NOTES: Decomposed Musk Thistle in the soil inhabits seed germination and growth of many native species, yet stimulates growth of its own seedlings.

NM COUNTIES: Basically statewide (not reported in Eddy, Harding, Luna, Sierra cos.)