Musk thistle, a member of the aster family, is an aggressive biennial plant with large, pink flowers on long, multi-branched stems. Musk thistle is native to western Europe and Asia and was introduced into the eastern United States in the early 1900s. It currently is present in forty states and is found widespread along railroad, highway, power line rights-of-way, and other disturbed areas. These areas become a refuge for invasion of crop and pasture lands and open natural areas. Musk thistle can grow readily in neutral to alkaline soils from sea level to an altitude of about 8000 ft. It prefers well drained soils and good sunlight. It impacts natural areas by colonizing sites of natural disturbances, where it may spread rapidly. Musk thistle is very sensitive to competition. It is listed as a noxious weed in many states.

Musk thistle stems are branched, very spiny, and grow to a height of 1.5 to 6 ft. The leaves are dark green, coarsely lobed, elliptic to lance shaped, and may be two to five inches long. The surface is waxy and smooth waxy, and there is a yellowish to white spine at the tip. Flowers form from early May to August. The flowers are 1.5 to 3.5 inches in diameter, purple, solitary, and have spines on the outer bracts. Large flowers droop at a 90-degree angle from the stem, the plant the common name of nodding thistle. Musk thistle plants may produce thousands of yellowish-brown seeds with attached plumes. Seed dissemination occurs approximately one month after the flowers form, and seeds may be wind blown for miles. Viable seeds may remain in the soil for over ten years. Musk thistle usually is biennial but occasionally will germinate and flower in a single year. Seedlings emerge in mid to late July and develop into a rosette up to 4 ft. accross. Plants overwinter in the rosette stage and begin to bolt in mid-March. During the bolting stage, plants form multi-branched stems that grow to 6 ft. in height. The number of seed heads formed on a plant is site dependent. As few as 1-18 heads may be produced on less favorable sites, while 241-561 may be produced on favorable sites. As many as 1200 seeds are produced per head, and 120,000 seeds per plant.