Native. Perennial. Propagates by seeds and by rootstocks. Time of bloom: June to August. Seed-time: July to September. Range: Western Ontario to the Northwest Territory and British Columbia, southward to Michigan, Kansas, New Mexico, and California. Habitat: All crops; most injurious in grain fields and meadows.
A very handsome plant, but one of the most obnoxious weeds of its family and very hard to suppress. Stem slender, round, smooth, two to three feet tall. Leaves exceedingly variable, oblong to lance-shaped in outline, but the lower ones deeply cut or pinnatifid, with segments turned backward and often having margined petioles; upper ones sessile and partly clasping, slightly toothed or entire, becoming linear near the top; all smooth and glaucous. The whole plant, even to its fleshy, light-colored rootstocks, is filled with bitter, milky juice. Heads in open racemes, lifted on rather long, scaly-bracted peduncles; they are about an inch broad, with numerous light blue rays, toothed at the tips; bracts of the involucre imbricated in three or four rows, the inner ones lance-shaped, the outer ones shortening to pointed ovate. Achenes flattened club-shaped, with ridged margins and finely grooved sides, tapering to a short, stiff beak tipped with a cup-like disk to which is attached a copious, silky, white pappus which enables the winds to sow the seed very widely. (Fig. 378.)
On the first appearance in any locality, it will pay to hand-pull or dig out the plants before seed production and before the rootstocks have penetrated far into the soil. Established root-stocks should be starved by persistent close cutting of all leaf-growth throughout the growing season. Where the land is badly infested, short rotations of cultivated crops - with very thorough tillage - are necessary if the weed is to be subdued.