As volunteer plants in the park go, this one is almost royalty. It’s Achillea millefolium, misleadingly labeled common yarrow, but there’s nothing common about it. Wikipedia says
In antiquity, yarrow was known as herbal militaris, for its use in stanching the flow of blood from wounds. Other common names for this species include gordaldo, nosebleed plant, old man’s pepper, devil’s nettle, sanguinary, milfoil, soldier’s woundwort, thousand-leaf, and thousand-seal.
It’s origin is probably Eurasia, but it’s been in California so long and is so widespread — it grows up to 3,500 feet and in every region except the deep desert — that Calflora, the censorious guardian of floral nativism, considers it native. In the wild it can spread rapidly and produce more than 43,000 plants per acre, but in the park here its spread is modest, occurring in isolated patches.
Yarrow is welcome in many gardens, and considerable work has been done to produce “improved” cultivars, some having pink or red flowers. The plant generally is prized for its drought tolerance and for erosion control. It’s also welcomed as a companion plant because it’s believed to repel bad insects and attract good ones, particularly ladybugs and hoverflies.
Yarrow also has an extensive history of traditional medicinal uses. Wikipedia:
Herbal and traditional uses
The herb is purported to be a diaphoretic, astringent, tonic, stimulant and mild aromatic. It contains isovaleric acid,salicylic acid, asparagin, sterols, flavonoids, bitters, tannins, and coumarins. The plant also has a long history as a powerful ‘healing herb’ used topically for wounds, cuts and abrasions. The genus name Achillea is derived from mythical Greek character, Achilles, who reportedly carried it with his army to treat battle wounds. This medicinal action is also reflected in some of the common names mentioned below, such as staunchweed and soldier’s woundwort.
In the Middle Ages, yarrow was part of a herbal mixture known as gruit used in the flavouring of beer prior to the use ofhops. The flowers and leaves are used in making some liquors and bitters.
Traditional names for A. millefolium include arrowroot, bad man’s plaything, bloodwort, carpenter’s weed, death flower, devil’s nettle, eerie, field hops, gearwe, hundred leaved grass, knight’s milefoil, knyghten, milefolium, milfoil, millefoil, noble yarrow, nosebleed, old man’s mustard, old man’s pepper, sanguinary, seven year’s love, snake’s grass, soldier, soldier’s woundwort, stanchweed, thousand seal, woundwort, yarroway, yerw. The English name yarrow comes from the Saxon (Old English) word gearwe, which is related to both the Dutch word gerw and the Old High German word garawa.
Yarrow has also been used as a food, and was very popular as a vegetable in the 17th century. The younger leaves are said to be a pleasant leaf vegetable when cooked like spinach, or in a soup. Yarrow is sweet with a slight bitter taste. The leaves can also be dried and used as a herb in cooking.
A. millefolium has seen historical use as a medicine, often because of its astringent effects.
Native American uses
Yarrow, Achillea millefolium and its North American varieties, was used in traditional Native American herbal medicine by tribes across the continent. The Navajo considered it to be a “life medicine”, chewed it for toothaches, and poured an infusion into ears for earaches. The Miwok in California used the plant as an analgesic and head cold remedy.
Several tribes of the Plains Indians used common yarrow. The Pawnee used the stalk for pain relief. The Chippewa used the leaves for headaches by inhaling it in a steam. They also chewed the roots and applied the saliva to their appendages as a stimulant. The Cherokee drank a tea of common yarrow to reduce fever and aid in restful sleep.
Among the Zuni people use the occidentalis variety medicinally. The blossoms and root are chewed, and the juice applied before fire-walking or fire-eating. A poultice of the pulverized plant is mixed with water and applied to burns. Recently it was reported that treatment with Achillea millefolium may attenuate disease severity, inflammatory responses, and demyelinating lesions in a mouse model of Multiple Sclerosis.
In rare cases, yarrow can cause severe allergic skin rashes; prolonged use can increase the skin’s photosensitivity. This can be triggered initially when wet skin comes into contact with cut grass and yarrow together.
In one study, aqueous extracts of yarrow impaired the sperm production of laboratory rats.
So there you have it. Next time you see Yarrow, omit the “common.”