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Yarrow
Achillea millefolium
Aster family (Asteraceae)

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All photos taken at the Klein Prairie -- Murrayville, Illinois, USA

Description: This introduced perennial plant is about 1-2' tall. It is unbranched, except near the apex, where the flowerheads occur. The central stem is light green, furrowed, and more or less covered with white cobwebby hairs. However, some plants may have glabrous stems. The alternate leaves are up to 6" long and 1" across, becoming smaller as they ascend the stems. Each fern-like leaf is narrowly ovate-oblong in outline and widest in the middle; however, it is pinnately compound in form and divided into linear segments. Each leaf segment is pinnately cleft or sharply toothed. The leaves are often crinkled or curled along their margins, folding upward along the central vein; but sometimes they are nearly flat. Like the stems, the leaves often have fine cobwebby hairs; the base of each leaf clasps the stem. The upper stems produce corymbs of small flowerheads. Each flowerhead is about " across, consisting of 5 ray white ray florets and a similar number of disk florets that are cream or pale yellow. The floral bracts are pale green and lanceolate-oblong; they often have cobwebby hairs. All parts of this plant exude a distinctive aroma that is somewhat soapy and astringent. The blooming period occurs from early to mid-summer and lasts about a month. Each floret is replaced by an achene that is oblong and somewhat flattened; it lacks a tuft of hairs. The root system produces abundant rhizomes and vegetative offsets.

Cultivation: The preference is full or partial sun, mesic to dry conditions, and a somewhat heavy clay-loam soil.

Range & Habitat: Yarrow is a common plant that has naturalized in all counties of Illinois (see Distribution Map). It is also cultivated in flower and herb gardens. Habitats include mesic to dry prairies, pastures, fallow fields, grassy waste areas, and edges of paths, yards, or hedges. Disturbed areas are preferred; Yarrow persists in native habitats to a limited extent. Yarrow was introduced into the United States from Europe as an ornamental and medicinal plant. However, a Western form of this species that is smaller in size and woollier in appearance may be native to North America.

Faunal Associations: The nectar of the flowers attracts many kinds of insects, especially flies and wasps. Among the flies are such visitors as bee flies, Syrphid flies (including Drone flies), Thick-headed flies, Tachinid flies, Flesh flies, Anthomyiid flies, and others. Halictid and other short-tongued bees occasionally visitor the flowers, where they suck nectar and collect pollen. Sometimes Mordella spp. (Tumbling Flower Beetles) are found on the flowerheads. Because the foliage of Yarrow has a bitter and biting taste, it is rarely consumed by most mammalian herbivores. However, sheep will eat it when the opportunity arises.

Photographic Location: Along the edge of a path at Judge Webber Park in Urbana, Illinois.

Comments: Among members of the Aster family, the fern-like foliage of Yarrow is rather unusual and it has a distinctive odor. Other members of the Aster family with this kind of foliage include Anthemis spp. (Mayweeds), Matricaria spp. (Chamomile), and Tanacetum vulgare (Tansy). Species of Mayweed and Chamomile produce daisy-like flowerheads that are much larger than the flowerheads of Yarrow; their flowerheads have more ray and disk florets. Tansy is a larger plant with medium to dark green foliage. While its flowerheads are about the same size as the flowerheads of Yarrow, they are bright yellow and lack ray florets.

Source:  http://www.illinoiswildflowers.info/weeds/plants/yarrow.htm

The text above is Copyright 2002-2005 by John Hilty.  All photography on this site is 2005 - 2006 by Kevin Klein.  Photo quality prints and permission for image use may be obtained by contacting the photographer at kklein@ic.edu.