Carduus nutans ssp. macrocephalus

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

Disturbed areas, roadsides.

June to October

Purple to white

16″ to 78″

This is a 16″ to 78″ tall, erect, biennial forb that rises on a single stem from a stout taproot.

The stems are erect, ribbed, and often branched near the top. They may be hairless or covered with short, soft, woolly, matted or tangled 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.

In the first year the plant appears as a rosette of basal leaves that may be 24″ or more in diameter. In the second year it sends up a single flowering stem.

Basal leaves are lance-shaped to broadly elliptic in outline and 4″ to 16″ long. In the first year they are shallowly pinnately lobed, sometimes with a whitish, waxy bloom (glaucous), and irregularly prickled. In the second year they become deeply pinnately lobed, each lobe again pinnately lobed. The primary lobes are cut up to 80% of the way to the midrib. The ultimate lobes are triangular-shaped and tipped with relatively hard, straw-colored spines. The upper side is dark green and moderately hairy with a light green midrib. The underside is moderately hairy. The margins are often whitish.

Stem leaves are similar, alternate, stalkless, and up to 12″ long, becoming smaller and less divided as they ascend the stem. The ultimate lobes are lance-shaped to egg-shaped. The base of the leaf continues down the stem and forms a pair of spiny wings. Upper stem leaves are lance-shaped and ½″ to 6″ long.

The inflorescence is a usually a single, short-stalked flower head at the end of the stem and each branch, sometimes a cluster of a few flower heads. The flower stalk is relatively naked—leafless and not winged—but sometimes has a few small, scattered bracts. It is often densely covered with felty hairs. The flower head nods (droops) ninety degrees when mature.

The whorl of bracts at the base of the flower head (involucre) is cup-shaped to somewhat bell-shaped, ¾″ to 2⅜″ long, and ¾″ to 2¾″ wide. The bracts of the involucre are lance-shaped to egg-shaped, spreading to bent backward, ⅝″ to 2″ long, 1 ⁄16″ to ¼″ wide, and sometimes purple at the tip. They are abruptly tapered to a 1 ⁄32″ to ⅛″ long spine at the tip.

The flower heads are ¾″ to 2¾″ wide. They have numerous purplish to white tubular flowers.

The fruit is a golden to brown, ⅛″ to 3 ⁄16″ long achene with whitish, barbed hairs attached.

Musk thistle (Carduus nutans ssp. leiophyllus) upper leaf surface is hairless. The lower leaf surface is hairless except for sometimes some hairs along the main veins. The flower stalks are long.

Musk thistle (Carduus nutans ssp. macrolepis) involucral bracts are evenly tapered, not abruptly tapered, at the tip. The upper leaf surface is hairless. The lower leaf surface is hairless except for sometimes some hairs along the main veins. The flower stalks are long.

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