Urtica dioica, commonly called stinging nettle, is a herbaceous perennial flowering plant, native to Europe, Asia, northern Africa, and North America, and is the best known member of the nettle genus Urtica.
Stinging nettles are a dioecious herbaceous perennial, growing to 1-2 m tall in the summer and dying down to the ground in winter. It has very distinctively yellow, widely spreading roots, rhizomes and stolons. The soft green leaves are 3-15 cm long are borne oppositely on an erect wiry green stem. The leaves have a strongly serrated margin, a cordate base and an acuminate tip with a terminal leaf tooth longer than adjacent laterals. It bears small greenish or brownish 4-merous flowers in dense axillary inflorescences. The leaves and stems are very hairy with non-stinging hairs and also bear many stinging hairs (trichomes), whose tips come off when touched, transforming the hair into a needle that will inject several chemicals: acetylcholine, histamine, 5-HT or serotonin, and possibly formic acid. This mixture of chemical compounds cause a sting or paresthesia from which the species derives its common name, as well as the colloquial names burn nettle, burn weed, burn hazel.
The taxonomy of stinging nettles has been confused, and older sources are likely to use a variety of systematic names for these plants. Formerly, more species were recognised than are now accepted. However, there are at least five clear subspecies, some formerly classified as separate species:
Other species names formerly accepted as distinct by some authors but now regarded as synonyms of U. dioica include U. breweri, U. californica, U. cardiophylla, U. lyalli, U. major, U. procera, U. serra, U. strigosissima, U. trachycarpa, and U. viridis. Other vernacular names include tall nettle, slender nettle, California nettle, jaggy nettle, burning weed, fire weed and bull nettle (a name shared by Cnidoscolus texanus and Solanum carolinense).
Stinging nettles are abundant in northern Europe and much of Asia, usually found in the countryside. It is less gregarious in southern Europe and north Africa, where it is restricted by its need for moist soil. In North America it is widely distributed in Canada and the United States, where it is found in every province and state except for Hawaii and also can be found in northernmost Mexico. In North America the stinging nettle is far less common than in northern Europe. The European subspecies has been introduced into North America as well as South America.
In the UK stinging nettles have a strong association with human habitation and buildings. The presence of nettles may indicate that a building has been long abandoned. Human and animal waste may be responsible for elevated levels of phosphate and nitrogen in the soil, providing an ideal environment for stinging nettles. This seems particularly evident in Scotland where the sites of crofts razed to the ground during the Highland Clearances can still be identified.
Nettles are the exclusive larval food plant for several species of butterfly, such as the Peacock Butterfly or the Small Tortoiseshell, and are also eaten by the larvae of some moths including Angle Shades, Buff Ermine, Dot Moth, The Flame, The Gothic, Grey Chi, Grey Pug, Lesser Broad-bordered Yellow Underwing, Mouse Moth, Setaceous Hebrew Character and Small Angle Shades. The roots are sometimes eaten by the larva of the Ghost Moth Hepialus humuli.
As Old English Stiðe, nettle is one of the nine plants invoked in the pagan Anglo-Saxon Nine Herbs Charm, recorded in the 10th century. Nettle is believed to be a galactagogue and a clinical trial has shown that the juice is diuretic in patients with congestive heart failure.
Urtication, or flogging with nettles, is the process of deliberately applying stinging nettles to the skin in order to provoke inflammation. An agent thus used is known as a rubefacient (i.e. something that causes redness). This is done as a folk remedy for rheumatism, as it provides temporary relief from pain.
Nettle leaf is a herb that has a long tradition of use as an adjuvant remedy in the treatment of arthritis in Germany. Nettle leaf extract contains active compounds that reduce TNF-α and other inflammatory cytokines. 
Nettle is used in hair shampoos to control dandruff, and is said to make hair more glossy, which is why some farmers include a handful of nettles with cattle feed. It is also thought nettles can ease eczema.
Nettle root extracts have been extensively studied in human clinical trials as a treatment for symptoms of benign prostatic hyperplasia (BPH). These extracts have been shown to help relieve symptoms compared to placebo both by themselves and when combined with other herbal medicines.
Fresh nettle is used in folk remedies to stop all types of bleeding, due to its high Vitamin K content. Meanwhile, in dry U. dioica, the Vitamin K is practically non-existent, and so is used as a blood thinner.
Not only does nettle leaf lower TNF-a levels, but it has been demonstrated that it does so by potently inhibiting the genetic transcription factor that activates TNF-a and IL-1B in the synovial tissue that lines the joint.
An extract from the nettle root (Urtica dioica) is used to alleviate symptoms of benign prostate enlargement. Nettle leaf extract, on the other hand, is what has been shown to reduce the pro-inflammatory cytokines TNF-a and IL-B1.
Cooking, crushing or chopping disables the stinging hairs. Stinging nettle leaves are high in nutrients, and the leaves can be mixed with other ingredients to create a soup rich in calcium and iron. Nettle soup is a good source of nutrients for people who lack meat or fruit in their diets. The young leaves are edible and make a very good pot-herb. The leaves are also dried and may then be used to make a tisane, as can also be done with the nettle's flowers.
Anti-itch drugs, usually in the form of creams containing antihistaminics or hydrocortisone, can provide relief from the symptoms of being stung by nettles. Many often ineffective folk remedies exist for treating the itching, including horsetail (Equisetopsida spp.), leaf of dock (Rumex spp.), Jewelweed, (Impatiens capensis and Impatiens pallida), mud, saliva, baking soda , calamine lotion,urine or soap and water. Some of these methods may provide some relief through mechanical stimulation such as rubbing or by cooling, or by the placebo effect.
In Great Britain the stinging nettle is the only common stinging plant, and has found a place in several figures of speech in the English language. To "nettle" someone is to annoy them. Shakespeare's Hotspur urges that "out of this nettle, (danger), we grasp this flower (safety)" (Henry IV, part 1, Act II Scene 3). The common figure of speech "to grasp the nettle" probably originated as a condensation of this quotation. It means to face up to or take on a problem that has been ignored or deferred. The metaphor may refer to the fact that if a nettle leaf is grasped firmly rather than brushed against, it does not sting so readily, because the hairs are crushed down flat and do not penetrate the skin so easily. In the German language, the idiom "sich in die Nesseln setzen", or to sit in nettles, means to get oneself in trouble.
Stinging Nettle has a flavour similar to spinach when cooked, and is rich in vitamins A, C, D, iron, potassium, manganese, and calcium. Young plants were harvested by Native Americans and used as a cooked plant in spring when other food plants were scarce. A soup made from the young shoots is considered a spring delicacy in Scandinavia. Cooking or drying completely neutralizes the toxic components found in this plant. Stinging Nettle should not be consumed after it enters its flowering and seed setting stages, as the leaves develop gritty particles called "cystoliths" which can irritate the urinary tract.
Soaking nettles in water will remove the stinging chemicals from the plant, which allows them to be handled and eaten without incidence of stinging. Young leaves generally have a better taste than older, more bitter leaves.
Nettles can be used in a variety of recipes, such as polenta and pesto. Nettle soup (or Nässelsoppa in Swedish) is a common use of the plant, particularly in Northern Europe. Young nettle leaves are similar in texture to spinach and other leafy greens, and can be substituted for or mixed with other greens in recipes.
The high protein content of nettles makes them nutritionally valuable for vegetarians.
Nettle stems contain a bast fibre that has been traditionally used for the same purposes as linen and is produced by a similar retting process. Unlike cotton, nettles grow easily without pesticides. The fibres are coarser however.
In recent years a German company started to produce commercial nettle textiles. 
As well being the fibre, Nettles were also used as a dye-stuff in the medieval period.