Invasive Species Council of Manitoba: Nodding Thistle

Nodding Thistle

(Carduus nutans)

Common Names: Nodding Thistle, Musk Thistle

Biennial or winter annual that reproduces by seed only. A native of Europe, nodding thistle has a long history as a rangeland pest.

The invasive nature of this aggressive plant can lead to severe degradation of native grasslands and meadows because grazing animals focus on native vegetation giving the thistles a competitive advantage.

It develops a long, fleshy taproot that becomes corky & h

Nodding Thistle

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w near the crown. Rosettes can be quite large. Several subspecies of Nodding Thistle occur in North America (e.g. Plumeless thistle), but there are no native thistles in the genus Carduus.

Habitat

Nodding Thistle grows from sea level to about 8,000 ft elevation, in neutral to acidic soils. It prefers disturbed areas but is still able to invade healthy plant communities.

Nodding Thistle can form tall, impenetrable thickets. It is not tolerant of excessively wet,dry or shady conditions.

Nodding Thistle Identification

Stems: First year forms a large rosette; second year grows between 20cm up to 2.5 m tall. Lower stems have spiny, lengthwise ridges. One or many stems can grow from one root crown.

Leaves: Leaves are alternate, deep green with a light green mid vein, waxy surface or sometimes long, hairy and deeply lobed with wavy,spiny edges up to 25 cm long. Leaf margins are often white. Leaves tend to clasp the stem.

Flowers: Flower heads are solitary at the ends of stems, about 3-5 cm in diameter and are composed of hundreds of tiny reddish-purple flowers. At the base of each head are several rows of spiny bracts. Flower heads commonly droop when mature, thus "Nodding Thistle."

A single flower head may produce 1,200 seeds.The plant dies after seed set.

Seed: Achenes 4-5 mm long, with longitudinal dotted stripes. Pappus bristles 13-25 mm long.

Prevention

Learn how to recognize this invasive plant in the early stages and the likelihood of eradicating it from your property is very good.