- Name also: Milfoil, Common Yarrow
- Family: Daisy Family – Compositae, subfamily Asteroideae
(formerly Aster Family – Asteraceae)
- Growing form: Perennial herb. With subterraneous runners.
- Height: 20–70 cm (8–28 in.). Stem varyingly soft-haired. Herb-like fragrance.
- Flower: Single flower-like, less than 5 mm (0.2 in.) capitula surrounded by involucral bracts. Capitula’s ray-florets (4–6) white (sometimes purple or pale purple), tongue-like, almost round, tip unclearly 2-toothed; disc florets white, tubular, small. Stamens 5. Pistil of 2 fused carpels. Involucre quite narrow, involucral bracts in several rows, smoothly hairy. Capitula borne in a dense corymbose cluster.
- Leaves: Alternate, usually stalkless. Blade 2–3 times pinnately lobed or with leaflets, lobes narrow, sharp-pointed, sparsely long-haired.
- Fruit: Glossy, with narrow and thick-winged achene.
- Habitat: Meadows, banks, yards, lawns, fields, pastures, wasteland, shores.
- Flowering time: July–September(–October).
Yarrow is one of the best-known of Finland’s meadow plants, as can be seen from the large amount of local names that have attached to it. It is common and abundant in open places where people are active. Apart from open forest pasture it can also survive in overgrown forest and it has also travelled along the sides of forest roads. On the other hand it can spread to form large patches on lawns, but it is unable to flower there.
Genus Achillea takes its name from the Ancient Greek stories about the invincible adventurer and hero Achilles. Yarrow has a long history as a medicinal herb for e.g. cramps, fevers and wounds that are not healing well, and it is still popular as a tea, also in Finland. It doesn’t suit everyone, however, as it can cause a rash on some people who merely make contact with it, and excessive internal doses can cause dizziness and headaches. Yarrow’s power comes from the bitter elements and volatile oil it contains, which give the shoots their characteristic herb-like smell. The flowers smell repellent, which is typical of plants that attract flies and beetles. Part of the seed that is produced by a pollinated plant stays on the plant and then spreads across the snow-crust in the winter. The seeds are also eaten during the winter by bullfinches, redpolls and many other small birds.
Ssp. millefolium is most common in the south and middle of Finland, and is replaced by ssp. sudetica in the north, and in fact the type species also grows commonly as an alien species in Lapland. Lapland’s yarrow could be a form that developed in northern Russia during the Ice Age and which has spread along stream banks to northern Finland as the ice-cap retreated. Sometimes a red-flowered form also grows in the wild – this is not an independent species or even subspecies but rather a hereditary form which only deviated from normal yarrow with regards to its colour. It is more common in ssp. sudetica and is cultivated in gardens as an ornamental.