Introduced. Annual or winter annual. Propagates by seeds. Time of bloom: June to August. Seed-time: July to September. Range: Nova Scotia to British Columbia, southward to Virginia, Indiana, and Nebraska. Also in Texas. Locally in other states. Habitat: Dry fields, pastures, roadsides, waste places.
This weed is the cause of much annoyance and loss to wool-growers. Sheep have carried it into many new localities, its presence in Texas being due to that agency. Stem one to two feet tall, erect, slender, branching at the top, gray with appressed hairs. Leaves narrow oblong to linear, entire, covered on both sides with fine, appressed, white hairs, sessile or the lowest spatu-late and tapering to short petioles. Flowers in terminal more or less one-sided, leafy-bracted racemes; the pedicels short, stout, not deflexed in fruit; corolla blue, hardly an eighth of an inch broad; stamens included; calyx five-pointed, enlarging and spreading as the burs mature; these are formed of the four nutlets, each about an eighth of an inch long, angled on the inner side, the other side rounded and having around the margin a double row of short spines tipped with star-shaped hooks. These spines break off readily, but the fruit can still be identified, when among other seeds, by its angles and the smooth space on the rounded side.
Late fall plowing for the purpose of destroying autumn plants. Pull or cut all flowering stalks before the first seeds ripen.