PLUMELESS THISTLE - Carduus acanthoides L.

Asteraceae - (Sunflower family)

In the fall a rosette of dark green leaves emerges from seed.  Leaves have hair on the underside with a light green mid vein on the upper side. The leaf margins are somewhat ruffled, deeply lobed or scalloped and have sharp reddish spines spaced evenly along edges.

The first year leaves developed a thick fleshy tap root. This root supports the second year rosette leaves and branching stems that may grow to 8 ft.  The alternate spiny stem leaves become smaller and fewer upward on the plant.  The bases of the leaves grow both up and downward blending onto the stem in what is called “wings,”  thus the whole plant becomes spiny.

The buds are deep bowl shaped and covered with narrow, upward pointing, dark tipped spines.  The flower petals protrude above and are Reddish-purple.  The 1 inch flowers are single or up to 5.  If the profusion of seeds do not blow away on the wind they fall to the ground to germinate and will last for up to 10 years in the soil. 

Habitat is limited because wildlife and livestock completely avoid areas infested with Plumeless thistle which may grow abundantly in overgrazed pastures, fields, valleys and roadsides.

The following is courtesy of Weeds of the West:
Plumeless thistle is a winter annual or biennial herb, from a stout fleshy taproot, rarely flowering the first year. Stems grow from 1 to 4 feet tall; they are freely branched above and covered with spiny wings 1/4 to 3/4 inch wide extending up to the flowering heads. Basal rosette leaves are usually 4 to 8 inches long with spinose lobes. Stem leaves alternate, sessile and blending into the stem. Peduncles usually spiny-winged up to the base of the flowering heads; heads solitary at the ends of branches or in clusters of 2 to 5. Involucral bracts narrowly lanceolate, sparsely to densely hairy. Corolla mostly purple, rarely white or yellowish.

This native of Eurasia is infrequent to locally abundant in pastures, stream valleys, fields and roadsides. It is frequently found in Idaho, Colorado and Wyoming and has the potential of becoming a widespread noxious weed. Flowering occurs from May to July.

(Courtesy of Weeds of the West)

No identified infestations in Fremont County.