Achillea millefolium, commonly known as yarrow () or common yarrow, is a flowering plant in the family Asteraceae. Other common names include old man's pepper, devil's nettle, sanguinary, milfoil, soldier's woundwort, and thousand seal. The plant is native to temperate regions of the Northern Hemisphere in Asia, Europe, and North America. It has been introduced as a feed for livestock in New Zealand and Australia. Description Achillea millefolium is an erect, herbaceous, perennial plant that produces one to several stems in height, and has a spreading rhizomatous growth form. Leaves are evenly distributed along the stem, with the leaves near the middle and bottom of the stem being the largest. The leaves have varying degrees of hairiness (pubescence). The leaves are long, bipinnate or tripinnate, almost feathery, and arranged spirally on the stems. The leaves are cauline, and more or less clasping, being more petiolate near the base. The inflorescence has 4 to 9 phyllaries and contains ray and disk flowers which are white to pink, blooming from March to October. There are generally 3 to 8 ray flowers, which are long and ovate to round. The tiny disk flowers range from 10 to 40. The inflorescence is produced in a flat-topped capitulum cluster and the inflorescences are visited by many insects, featuring a generalized pollination system. The small achene-like fruits are called cypsela. The plant has a sweet scent similar to that of chrysanthemums, so powerful that it may be irritating to some. Chemistry The dark blue essential oil of yarrow contains chemicals called proazulenes. Chamazulene and δ-Cadinol are chemical compounds found in A. millefolium. The chromophore of azulene was discovered in yarrow and wormwood and named in 1863 by Septimus Piesse. Yarrow contains isovaleric acid, salicylic acid, asparagine, sterols, and flavonoids. It also contains phenolic acids such as gallic acid, 3, 4-dihydroxy benzoic acid, 2-OH-Benzoic acid, chlorogenic acid, vanillic acid, caffeic acid, syringic acid, p-coumaric acid, sinapic acid, ferulic acid, cinnamic acid and flavonoid such as myricetin, hesperidin, quercetin, luteolin, kaempferol, apigenin, rutin, hyperoside. Taxonomy The several varieties and subspecies include: Achillea millefolium subsp. millefolium A. m. subsp. m. var. millefolium – Europe, Asia A. m. subsp. m. var. borealis – Arctic regions A. m. subsp. m. var. rubra – Southern Appalachians A. millefolium subsp. chitralensis – western Himalaya A. millefolium subsp. sudetica – Alps, Carpathians Achillea millefolium var. alpicola – Western United States, Alaska Achillea millefolium var.