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 and by rootstocks. Time of bloom: June to October.
Seed-time: August to November.
Range: Throughout North America, and in most parts of the world. Habitat: Meadows, pastures, roadsides, and waste places.
A most hardy weed, thriving in nearly any kind of soil and indifferent to tropic heat or arctic cold; well named for the invulnerable Achilles, who is said to have used the herb for the cure of his Myrmidons wounded at the siege of Troy. However that may be, the plant is still valued medicinally and its dried leaves and flowers bring three to five cents a pound in the drug market.
Stem one to two feet tall, stiffly erect, simple or sometimes forked above, webby-haired or nearly smooth. Leaves alternate, the lower ones sometimes ten inches long, lance-shaped in outline, deep green, twice pinnatifid and the segments finely toothed; stem leaves less divided, narrow and sessile; the foliage is strong-scented, its taste biting and bitter.
Fig. 338. - Yarrow (Achillea Millefolium). X 1/4.
Cattle usually avoid the plant when green, but sometimes eat it with dry fodder, and then it is very damaging to the quality of dairy products. Flowers in dense, flat-topped, stiffly branched, compound corymbs, the heads very small, white or sometimes pink; rays and disk-florets both fertile; bracts of the involucre, imbricated, with scarious margins. Achenes flattened oblong, without pappus. (Fig. 338.)
The rootstocks are horizontal and tough, and cling rather strongly to the parent plant, so that sometimes when the ground is soft one may oust a whole colony at a pull - the young shoots of the first year being mere tufts of plume-like leaves. Prevent seed production by close cutting before the first flowers mature. In cultivated crops the weed is suppressed by the required tillage.