Plumeless thistle

(Carduus acanthoides)

Winter annual or biennial, spine covered thistle growing to 0.3 to 1.2 m tall. Introduced from Eurasia.

Quick Identification:

• Small reddish-purple flower heads.
• Stem leaves are hairy only on the upper side.
• Spiny wings densely covering stem up to base of flower heads.
• Narrow bracts below the seed head appear as sharp spines.

Interesting Facts:

Unpalatable to grazing animals.

Management:

Hand pulling or digging is effective if root crown is removed. Best done when soil is moist. Wear gloves, avoid skin contact. If any portion of flower is beginning to emerge, or if seed heads are formed, pick, bag, and remove. Selective herbicides are effective.

Plumeless thistle flower and seeds

Plumeless thistle plant

Plumeless thistle flowers

Plumeless thistle flower and seeds

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Flowers:

Small reddish-purple flowers (less than 3 cm in diameter) are either solitary or in clusters of two to five. Narrow bracts below the seed head appear as sharp spines.

Leaves and Stems:

Leaves have hair only on the underside, spines along the leaf margin, and a light coloured midrib. Stem leaves are stalkless and extend down the stem like spiny wings. The stems are branched near the top and are densely covered with spiny wings up to base of flower heads. Rosette leaves are deeply serrated nearly to the midrib.

Reproduction and Dispersal:

Reproduces by seed only. Dispersed primarily by wind. Extremely prolific seed producer; up to 9,000 seeds per plant.

Seeds:

Single seeded fruits are 2 to 3 mm long, light brown with faint longitudinal stripes, and have a plume (pappus) with bristles 11 to 12 mm long.

Habitat Preference:

Pastures, grasslands, crop fields, river valleys, roadsides and disturbed open sites.

Roots:

Large, fleshy taproot.

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