Carduus acanthoides

Native of Asia and Europe. Introduced and naturalized in North America.

Minnesota prohibited noxious weed, invasive

Pastures, disturbed areas, roadsides.

July to October

Purple

12″ to 60″

This is a 12″ to 60″ tall, erect, biennial forb that rises on a single stem from a long, stout, fleshy taproot.

In the first year the plant appears as a dense rosette of basal leaves. In the second year it sends up a single flowering stem.

The stems are erect, ribbed, and freely branched near the top. They may be hairless or lightly covered with soft, long, unmatted hairs. They have small appendages (wings) running the length of the stem and branches except just below the inflorescence. The wings are interrupted, not continuous for the length of the stem. They are irregularly lobed and wavy, each lobe tipped with relatively hard, straw-colored spines.

Basal leaves are lance-shaped to elliptic in outline and 4″ to 8″ long. They are deeply pinnately lobed. The lobes are irregular and also toothed or lobed. The ultimate lobes or teeth are tipped with relatively hard, straw-colored spines. The upper and lower surfaces are green and sometimes hairless, usually sparsely covered with long, soft, shaggy, unmatted hairs mostly along the main veins.

Stem leaves are similar, alternate, and stalkless, becoming smaller and less divided as they ascend the stem. The base of the leaf continues down the stem and forms a pair of spiny wings. Upper stem leaves are lance-shaped and unlobed.

The inflorescence is a usually a single flower head, sometimes a cluster of 2 to 5 flower heads, held erect at the end of the stem and each branch. The heads may be unstalked or at the end of a long, spiny-winged stalk.

The whorl of bracts at the base of the flower head (involucre) is ⅜″ to 1″ in diameter and in the shape of half of a sphere. The bracts of the involucre are narrowly lance-shaped, erect or loosely spreading, and no more than 1 ⁄16″ wide. The middle and outer bracts have long spines at the tip.

The flower heads are ½″ to 1″ wide. They have numerous purple, tubular flowers.

The fruit is a golden to brown, 1 ⁄16″ to ⅛″ long achene with whitish, minutely barbed hairs attached.

Musk thistle (Carduus nutans) is a larger plant. The basal leaves are longer, up to 16″ long. The upper side of the leaf is hairless. The flower stalk is usually naked, not winged, but sometimes has a few small, scattered bracts. The flower head droops ninety degrees when mature. The flower heads are much larger, ¾″ to 2¾″ wide.