Western Yarrow (Achillea millefolium L. var. occidentalis DC.)

Alternate Names: Woolly yarrow

Photographic Location: Sycamore Ridge Ranch in Middle TN.

General: Western yarrow is a member of the Asteraceae (Sunflower) family that is commonly found in natural and disturbed habitats throughout the western U.S. It is a self-incompatible, insect-pollinated species occurring as native forms that may differ in chromosome number.

Conservation: Western yarrow is an early successional species that readily establishes on disturbed sites. It is recommended for adding species diversity in native seed mixtures for rehabilitation of disturbed sites such as rangelands, mined lands, roadsides, park and restoration areas, prairie reconstruction projects, and farm bill program conservation plantings. Secondary use is for ornamental application in pollinator friendly, low maintenance, or naturalized landscapes.

Forage: Western yarrow is a food source for bighorn sheep, pronghorn antelope, and deer. Sage-grouse, especially chicks, and other upland birds rely heavily on the foliage of western yarrow as a food source. Sage-grouse chicks also benefit from eating the insects associated with yarrow. In Montana, domestic sheep and goats derive approximately 40 percent of their summer diet from western yarrow, while it constitutes 20 percent of cattle and horse diets (Reitz and Morris, 1939). The leaves and flowers contain volatile oils, alkaloids, and glycosides that are considered toxic, but the plant is seldom overgrazed and eaten in large enough quantities to be harmful to foraging animals.

Ethnobotanic: Native Americans used western yarrow for many purposes, such as a tea to cure stomach ailments, a poultice on infected wounds, and as a mosquito repellant.

Weediness: Western yarrow is not to be confused with the introduced, invasive plant, common yarrow (Achillea millefolium var. millefolium). Common yarrow has origins in central Asia, the European continent, and the islands of Scandinavia. It is considerably different from western yarrow in that it has a much taller stature, aggressive vigor, and weedy characteristics. Common yarrow also initiates a later sequence of flowering and seed ripening. Western yarrow is a common component of western rangelands and only under definite conditions of overgrazing and disturbance could it become locally abundant. Yarrow is seldom regarded as a problem weed except on heavily disturbed, arable sites with favorable environmental conditions.