This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Native. Perennial. Propagates by seeds.
Time of bloom: June to September.
Seed-time: July to October.
Range: Illinois and Minnesota to the Saskatchewan, southward to Texas and Mexico, and westward to California. Habitat: Meadows, grain fields, waste places, and roadsides.
This weed was formerly common only on the western prairies, but unrestricted exchange of commercial seeds has carried it into many of the Eastern States as an impurity of grass seeds and grain. It is very persistent when established in meadow lands and is a serious injury to the crop. The leaves and flowering tops of the weed are official in the United States Pharmacopoeia, and, if collected when the flowers are just coming into full bloom and quickly dried, are worth in the drug market five to ten cents a pound.
Stem and branches somewhat reddish, smooth, erect, freely branching, ten inches to two feet high. Leaves alternate, oblong or the lower ones spatulate, blunt-pointed, sessile, more or less clasping at the base, spinescently toothed. Heads terminal, solitary, about an inch broad, resinously viscid; bracts of the involucre imbricated in several rows, awl-tipped, green, spreading, and recurved; the outer row of strap-shaped or ray florets are pistillate and fertile, disk florets perfect. Achenes light-colored, short,thick, slightly flattened and curved, obscurely four-sided, marked with lengthwise lines or ribs; pappus consists of two or three barbed awns. (Fig. 293.)
Sow clean seed. Prevent reproduction by cutting before any seed has ripened. Where the infestation is new and areas are small, grubbing out or hand-pulling of the perennial roots is well worth the labor; but rankly infested fields require to be put under cultivation.