Introduced. Perennial. Propagates by seeds and by rootstocks. Time of bloom: June to August. Seed-time: July to September. Range: Newfoundland and Nova Scotia to Manitoba and the Dakotas, southward to New Jersey and Illinois. Habitat: Grain fields, cultivated crops, roadsides, waste places.
A most noxious weed because of the creeping, horizontal root-stocks extending in all directions and putting forth new plants and roots at the joints; these rootstocks are rather thick, yellowish white, and, like all the rest of the plant, filled with a milky and bitter juice. Stems two to four feet tall, stout, smooth, finely grooved, hollow between joints. Leaves pinnatifid, the terminal lobe large, pointed, the lateral lobes turned backward and decreasing in size toward the base; the lower and basal leaves narrowing to margined petioles, the upper ones sessile and clasping by a heartshaped base, all dark green, waxy-smooth, toothed with weak spines. Heads in large corymbose clusters, deep yellow, nearly two inches broad, the long rays five-toothed, the bracts of the involucre and the pedicels usually set with stiff, glandular hairs, though in some localities a smooth and glaucous variety is common. Achene brown, about an eighth of an inch long, compressed, with wrinkled lengthwise ridges, and tufted with very copious, fine, white pappus. (Fig. 371.)
Short rotations of hoed crops, receiving very frequent, thorough, and late tillage, are necessary in order to clear the ground of this weed. It is not harmed by any spray. Horse cultivation serves only to break and spread the rootstocks. Complete prevention of food-assimilating green growth above ground is the only sure remedy.