Plumeless Thistle

Carduus acanthoides L.

Asteraceae (Sunflower Family)

▲ ▼ first year rosettes just before bolting

▲ ▼ flowering plants

▲ ▼ flower buds

▲ ▼ inflorescences

▲ ▼ flowers, showing winged, spiny stems and narrow outspread bracts below head inflorescences

▲ ▼ inflorescences with pointed bracts

▲ comparison between plumeless thistle flower (left) and musk thistle flower (right)

Carduus acanthoides L., Plumeless Thistle: (Bayer Code: CRUAC; US Code: CAAC)

Biennial thistle very similar to musk thistle, except first year leaves are more narrow and deeply lobed, with more marginal spines
Second-year flowering stem is moderately branched, with smaller leaves
Flowers are smaller than musk thistle, (0.5-1.5 inches diameter) with more lanceolate/linear flat bracts, rather than triangular bracts seen on musk thistle
No ray flowers, and disk flowers are pink to purplish
Flowering season is late spring to early summer (May-June), which differs from other invasive thistles (Canada thistle, bull thistle) that tend to bloom in mid to late summer (July-September)
Found in pastures, along roadsides; more common in northern Midwest

(Updated January 23, 2019)