(Achillea millefolium) Common Yarrow

Achillea millefolium, commonly known as yarrow or common yarrow is a flowering plant in the family Asteraceae. It 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 places like New Zealand and Australia, where it is a common herb of both wet and dry areas, such as roadsides, meadows, fields and coastal places.

In New Mexico and southern Colorado, it is called plumajillo (Spanish for 'little feather') from its leaf shape and texture. 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.

Description 
Clusters of 15 to 40 tiny disk flowers surrounded by three to eight white to pink ray flowers are, in turn, arranged in a flat-topped inflorescence (Wenatchee Mountains, Washington).

Achillea millefolium is an erect, herbaceous, perennial plant that produces one to several stems 0.2–1 m (0.66–3.28 ft) 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 5–20 cm (2.0–7.9 in) long, bipinnate or tripinnate, almost feathery, and arranged spirally on the stems. The leaves are cauline, and more or less clasping. 

The inflorescence has 4 to 9 phyllaries and contains ray and disk flowers which are white to pink. The generally 3 to 8 ray flowers are ovate to round. Disk flowers range from 15 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 strong, sweet scent, similar to that of chrysanthemums.

Distribution and habitat 
Yarrow grows from sea level to 3,500 metres (11,500 ft) in elevation. The plant commonly flowers from May to July. Common yarrow is frequently found in the mildly disturbed soil of grasslands and open forests. Active growth occurs in the spring. 

The plant is native to Eurasia and is found widely from the UK to China.

In North America, both native and introduced genotypes, and both diploid and polyploid plants are found. It is found in every habitat throughout California except the Colorado and Mojave Deserts. Common yarrow produces an average yield of 43,000 plants per acre, with a total dry weight of 10,500 lbs.

The plant is found in Australia as an introduction.

Ecology
Birds 
Several cavity-nesting birds, including the common starling, use yarrow to line their nests. Experiments conducted on the tree swallow, which does not use yarrow, suggest that adding yarrow to nests inhibits the growth of parasites. 

Insects
Achillea millefolium is a food source for many species of insects.

Moths
The larvae of the moths Bucculatrix clavenae, B. cristatella, B. fatigatella, B. humiliella, B. latviaella, Cnephasia abrasana, Cochylimorpha elongana, Coleophora argentula, C. carelica, C. ditella, C. expressella, C. follicularis, C. gardesanella, C. millefolii, C. partitella, C. ptarmicia, C. quadristraminella, C. succursella, C. vibicigerella, Depressaria olerella, D. silesiaca, Dichrorampha alpinana (broad-blotch drill), D. petiverella, D. vancouverana (tanacetum root moth), Eupithecia millefoliata (yarrow pug), E. nanata (narrow-winged pug), Gillmeria pallidactyla, Idaea pallidata, Isidiella nickerlii, Loxostege manualis, Phycitodes maritima, P. saxicola, Pyncostola bohemiella, Sophronia sicariellus and Thetidia smaragdaria (Essex emerald) feed on Achillea millefolium in Europe.
The larvae of Chlorochlamys chloroleucaria (blackberry looper), Coleophora quadruplex and Sparganothoides lentiginosana (lentiginos moth) feed on A. millefolium in North America.
Other species of moths with a more cosmopolitan distribution include Aethes smeathmanniana (Smeathmann's aethes moth), Chloroclystis v-ata (v-pug), Choristoneura diversana, Cochylidia richteriana, Epiblema graphana, Eupithecia succenturiata (bordered pug), E. vulgata (common pug), Jordanita budensis and Thiodia citrana (lemon bell).

Beetles
Cassida denticollis, Galeruca tanaceti, Hypocassida subferruginea and Phytoecia virgula are cosmopolitan species of beetles that feed on A. millefolium.

Chrysanthia viridissima is a European species whose adults can be found feeding on pollen and nectar.
Trichodes ornatus (ornate checkered beetle) is a species found in North America whose adults can be found feeding on A. millefolium.

True Bugs
Horistus orientalis is a species of plant bugs that feed on A. millefolium.

Wasps
Hedychrum rutilans is a species of cuckoo wasps whose adults can be found feeding on A. millefolium in Europe and North Africa.

Cultivation
Achillea millefolium is cultivated as an ornamental plant by many plant nurseries. It is planted in gardens and natural landscaping settings of diverse climates and styles. They include native plant, drought-tolerant, and wildlife gardens. The plant is a frequent component of butterfly gardens. The plant prefers well-drained soil in full sun, but can be grown in less ideal conditions.

Propagation 
For propagation, seeds require light for germination, so optimal germination occurs when planted no deeper than one-quarter-inch (6 mm). Seeds also require a germination temperature of 18–24 °C (64–75 °F). It has a relatively short life in some situations, but may be prolonged by division in the spring every other year, and planting 12 to 18 in (30–46 cm) apart. It can become invasive.

Uses
Its essential oil contains chemicals called proazulenes.The dark blue essential oil kills the larvae of the mosquito Aedes albopictus. 

Opopanax, also known as opobalsam, refers to a number of gum resins, including the one from A. millefolium. It is traditionally considered to have medicinal properties.

Some pick-up sticks are made of yarrow.

Companion planting
Yarrow is considered an especially useful companion plant, repelling some pest insects while attracting good, predatory ones. It attracts predatory wasps, which drink the nectar and then use insect pests as food for their larvae. Similarly, it attracts ladybirds and hoverflies.

Agriculture 
A. millefolium can be planted to combat soil erosion due to the plant's resistance to drought. Before the arrival of monocultures of ryegrass, both grass leys and permanent pasture always contained A. millefolium at a rate of about 0.3 kg/ha. At least one of the reasons for its inclusion in grass mixtures was its deep roots, with leaves rich in minerals. Thus its inclusion helped to prevent mineral deficiencies in the ruminants to which it was fed.

It was introduced into New Zealand as a drought-tolerant pasture. It is very prevalent. 

Food 
In the Middle Ages, yarrow was part of a herbal mixture known as gruit used in the flavoring of beer prior to the use of hops.The flowers and leaves are used in making some liquors and bitters. 

Herbal and traditional uses
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. A. millefolium has seen historical use as in traditional medicine, often because of its astringent effects. The herb is purported to be a diaphoretic, astringent, tonic, stimulant and mild aromatic. It contains isovaleric acid, salicylic acid, asparagine, sterols, and flavonoids. The genus name Achilles is derived from mythical Greek character, Achilles, who reportedly carried it with his army to treat battle wounds. This medicinal use is also reflected in some of the common names mentioned below, such as staunchweed and soldier's woundwort.

Yarrow and tortoiseshell are considered to be lucky in Chinese tradition. 

In classical Greece, Homer tells of the centaur Chiron, who conveyed herbal secrets to his human pupils, and taught Achilles to use yarrow on the battle grounds of Troy. 

British folklore 
In the Hebrides a leaf held against the eyes was believed to give second sight. 

Chinese divination
The stalks are dried and used as a randomising agent in I Ching divination. 

Native American uses
Yarrow and its North American varieties were traditionally used by many Native American nations across the continent. The Navajo historically considered it a "life medicine" and chewed the plant for toothaches and used its infusions for earaches. The Miwok in California use the plant as an analgesic and head cold remedy.

Common yarrow is used by Plains Indigenous peoples, such as the Pawnee, who use the stalk for pain relief. The Cherokee drink a tea of common yarrow to reduce fever and aid in restful sleep. 

The occidentalis variety is used medicinally by the Zuni people. 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. 

The Ojibwe people historically sprinkled a decoction of yarrow leaves on hot stones and inhaled it to treat headaches,as well as applied decoctions of the root onto skin for its stimulant effect.They also smoked its florets for ceremonial purposes, as well as placed them on coals and inhaled their smoke to break fevers.

It has also been used to treat hemorrhaging, as a poultice to ease rashes, and as a tea made from the leaves to cure stomach ailments. 

Dangers
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.

According to the ASPCA, yarrow is toxic to dogs, cats, and horses, causing increased urination, vomiting, diarrhea and dermatitis. 

In a standard rodent model for reproductive toxicity, aqueous extracts of yarrow produced a significant increase in the percentage of abnormal sperm. 

Chemistry
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.
en.wikipedia.org 

https://en.wikipedia.org/wiki/Achillea_millefolium