This section is from the book "Nature's Garden", by Neltje Blanchan. Also available from Amazon: Nature's Garden; An Aid To Knowledge Of Our Wild Flowers And Their Insect Visitors.
Flower-heads - Grayish-white, rarely pinkish, in a hard, close, flat-topped, compound cluster. Ray florets 4 to 6, pistillate, fertile; disk florets yellow, afterward brown, perfect, fertile. Stem: Erect, from horizontal rootstalk, 1 to 2 ft. high, leafy, sometimes hairy. Leaves: Very finely dissected (Millefolium = thousand leaf), narrowly oblong in outline.
Preferred Habitat - Waste land, dry fields, banks, roadsides.
Flowering Season - June - November.
Distribution - Naturalized from Europe and Asia throughout North America.
Everywhere this commonest of common weeds confronts us; the compact, dusty-looking clusters appearing not by waysides only, around the world, but in the mythology, folk lore, medicine, and literature of many peoples. Chiron, the centaur, who taught its virtues to Achilles that he might make an ointment to heal his Myrmidons wounded in the siege of Troy, named the plant for this favorite pupil, giving his own to the beautiful blue corn-flower (Centaurea Cyanus). As a love-charm; as an herb-tea brewed by crones to cure divers ailments, from loss of hair to the ague; as an inducement to nosebleed for the relief of congestive headache; as an ingredient of an especially intoxicating beer made by the Swedes, it is mentioned in old books. Nowadays we are satisfied merely to admire the feathery masses of lace-like foliage formed by young plants, to whiff the wholesome, nutty, autumnal odor of its flowers, or to wonder at the marvellous scheme it employs to overrun the earth.
Like the daisy, each small flower in a cluster, as symmetrically arranged as brain coral, is made up of a large number of minute but perfect florets, suited to attract insects by making a better show than each could do alone, and by offering them accessible feeding places close together, where they may feast with minimum loss of time. Simultaneous cross-fertilization of many florets must be effected by every visitor crawling over a cluster. The florets in each disk open in regular array toward the centre. At the expense of stamens, which are absent in the grayish-white ray florets, they have attained their development, another instance of "progress by loss " from the evolutionary standpoint. By prolonging its season of bloom to get relief from the fierce competition for insect visitors in midsummer; by increase through seeds, and runners too; by contenting itself with neglected corners of the earth, the yarrow gives us many valuable lessons on how to succeed.
Yarrow (Achillea Millefolium)