Asteraceae (Sunflower family)
This native of Eurasia is infrequent to locally abundant in pastures, stream valleys, fields and roadsides. It is found in Idaho, Colorado and Wyoming and has the potential of becoming a widespread noxious weed.
Growth Habit: Winter annual or biennial, 1 to 4 feet tall, freely branched above and covered with spiny wings.
Leaves: Basal rosette leaves are usually 4 to 8 inches long with spiny lobes. Stem leaves alternate, blending into the stem. Peduncles are usually spiny-winged up to the base of the flowering heads.
Flowers: 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 five. Their seeds, which blow in the wind or fall to the ground, can remain viable for up to 10 years in the soil.
Other: Wildlife and livestock avoid areas infested with plumeless thistle.