Canada thistle is a member of the Aster family and was introduced from Europe. It is a creeping perennial, which reproduces by seeds and fleshy, horizontal roots. The erect stem is hollow, smooth and slightly hairy, one to five feet tall, simple, and branched at the top. The flower color is primarily lavender, pink, or purple. It is one of the most widespread and economically damaging noxious weeds in Colorado.
Infestations are found in cultivated fields, riparian areas, pastures, rangeland, forests, lawns and gardens, roadsides, and in waste areas. Because of its seeding habits, vigorous growth, and extensive underground root system, control and eradication are difficult. Canada thistle emerges in May and is common throughout most parts of Garfield County.