Nettle
Nettle is the common name for any of between 30-45 species of flowering plants of the genus Urtica in the family Urticaceae, with a cosmopolitan though mainly temperate distribution. They are mostly herbaceous perennial plants, but some are annual and a few are shrubby.
The most prominent member of the genus is the stinging nettle Urtica dioica, native to Europe, north Africa, Asia, and North America. The genus also contains a number of other species with similar properties, listed below. However, a large number of species names that will be encountered in this genus in the older literature (about 100 species have been described) are now recognised as synonyms of Urtica dioica. Some of these taxa are still recognised as subspecies.
Most of the species listed below share the property of having stinging hairs, and can be expected to have very similar medicinal uses to the stinging nettle. The stings of Urtica ferox, the ongaonga or tree nettle of New Zealand, have been known to kill horses, dogs and at least one human.
The nature of the toxin secreted by nettles is not settled.  The stinging hairs of most nettle species contain formic acid, serotonin and histamine; however recent studies of Urtica thunbergiana (Fu et al, 2006) implicate oxalic acid and tartaric acid rather than any of those substances, at least in that species.

# Species of nettle
Species in the genus Urtica, and their primary natural ranges, include:
- Urtica angustifolia Fisch. ex Hornem. 1819. China, Japan, Korea.
- Urtica ardens. China.
- Urtica atrichocaulis. Himalaya, southwestern China.
- Urtica atrovirens. Western Mediterranean region.
- Urtica cannabina L. 1753. Western Asia from Siberia to Iran.
- Urtica chamaedryoides (heartleaf nettle). Southeastern North America.
- Urtica dioica L. 1753 (stinging nettle or bull nettle). Europe, Asia, North America.
- Urtica dubia (large-leaved nettle). Canada.
- Urtica ferox (ongaonga or tree nettle). New Zealand.
- Urtica fissa. China.
- Urtica galeopsifolia Wierzb. ex Opiz, 1825. Central and eastern Europe.
- Urtica gracilenta (mountain nettle). Arizona, New Mexico, west Texas, northern Mexico.
- Urtica hyperborea. Himalaya from Pakistan to Bhutan, Mongolia and Tibet, high altitudes.
- Urtica incisa (scrub nettle). Australia.
- Urtica kioviensis Rogow. 1843. Eastern Europe.
- Urtica laetivirens Maxim. 1877. Japan, Manchuria.
- Urtica mairei. Himalaya, southwestern China, northeastern India, Myanmar.
- Urtica membranacea. Mediterranean region, Azores.
- Urtica morifolia. Canary Islands (endemic).
- Urtica parviflora. Himalaya (lower altitudes).
- Urtica pilulifera (Roman nettle). Southern Europe.
- Urtica platyphylla Wedd. 1856-1857. China, Japan.
- Urtica pubescens Ledeb. 1833. Southwestern Russia east to central Asia.
- Urtica rupestris. Sicily (endemic).
- Urtica sondenii (Simmons) Avrorin ex Geltman, 1988. Northeastern Europe, northern Asia.
- Urtica taiwaniana. Taiwan.
- Urtica thunbergiana. Japan, Taiwan.
- Urtica triangularis
- Urtica urens L. 1753 (dwarf nettle or annual nettle). Europe, North America.
The family Urticaceae also contains some other plants called nettles that are not members of the genus Urtica. These include the wood nettle Laportea canadensis, found in eastern North America from Nova Scotia to Florida, and the false nettle Boehmeria cylindrica, found in most of the United States east of the Rockies. As its name implies, the false nettle does not sting.
There are many unrelated organisms called nettle, such as:
- Dead-nettle (Lamium spp.) and hedge-nettle (Stachys spp.) which are in the Lamiaceae or mint family.
- Devil's nettle, which is another name for yarrow.
- Carolina horsenettle (Solanum carolinense) in the Solanaceae.
- Spurge-nettle (Cnidolscolus stimulosus) in the Euphorbiaceae.
- Sea nettle (Chtysaora quinquecirrha) which is a jellyfish.
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.

# Uses

## Culinary
The tops of growing nettles are a popular cooked green in many areas. Some cooks throw away a first water to get rid of the stinging compounds, while others retain the water and cook the nettles straight. Nettle tops are sold in some farmers' markets and natural food stores.

## Tea
The fresh or dried leaves of nettle can be used to make a tea and commercial tea bags are commonly sold in natural food stores.

## Medical
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. They may also be used as a suppository, although this can be very painful and will not stop much skin irritation.
Extracts can be used to treat arthritis, anemia, hay fever, kidney problems, and pain. 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.
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.
Because it contains 3,4-divanillyltetrahydrofuran, certain extracts of the nettle are used by bodybuilders in an effort to increase free testosterone by occupying sex-hormone binding globulin.
Fresh nettle, specifically Urtica Dioica, is used in folk remedies to stop all types of bleeding, due to its high Vitamin K content. Meanwhile, in dry Urtica Dioica, the Vitamin K is practically non-existent, and so is used as a blood thinner.

## Paper
Nettle stems are a popular raw material used in small-scale papermaking.

## Textiles
Nettle fibre has been used in textiles.  This is more experimental than mass-market.  Unlike cotton, nettles grow easily without pesticides.  The fibres are coarser however. 
As well being the fibre, Nettles were also used as a dye-stuff in the medieval period.

# Safety
Though the fresh leaves can cause painful stings and acute urticaria, these are rarely seriously harmful (but see remarks in the introductory section re the U. ferox, ongaonga or tree nettle of New Zealand). Otherwise most species of nettles are extremely safe and some are even eaten as vegetables after being steamed to remove the stingers.
Nettles can be picked painlessly by wearing a standard pair of washing-up gloves.  Another common recommendation is to firmly grasp the nettle with the bare hand, crushing the stingers instead of allowing them to penetrate the skin.  Done properly, this is effective in practice, however due to a natural hesitancy when grabbing a nettle, first time practitioners close their hand too gently and slowly and so get stung. A traditional verse goes "Tenderly you stroke a Nettle, and it stings you for your pains. Grasp it like a man of mettle, and it soft as silk remains."
The traditional remedy for nettle stings is rubbing with the crushed leaf of the dock plant, Rumex obtusifolius, which often grows beside nettles in the wild and has a milky substance which can cause dermatitis. Plantain is another traditional remedy. The alkalinity of the sap may counteract the nettle's acids.  Nettle itself will release alkaline sap when macerated While there is no scientific proof that this remedy works, searching for and using a dock leaf at least takes the mind off the stinging pain somewhat. Though unproven, some claim that dabbing mud on the affected area, allowing it to dry, and rubbing it off can remove the stingers. Another disputed claim is that the spores of certain ferns can lessen the pain by rubbing the underside of fern leaves, where the spores are located in rows of round, orange lumps, on the affected area.
The nettle stingers can be removed from the skin quickly and effectively by wiping your skin with a chamois (same as used for drying cars).  The inside of a leather glove works similarly.  The nettle hairs stick to these textures more readily than your skin and a simple single wiping removes them from your skin.

# Popular culture
- The Bottle Inn, a pub in Marshwood, Dorset, England, holds an annual World Stinging Nettle Eating Championship.  The women's title is currently held by Jo Carter, of Weymouth, who ate the leaves from 34 feet of raw stinging nettles in the 2006 competition.  The men's title is held by veteran competitor Simon Sleigh, who chomped the leaves from more than 74 feet of stinging nettles in an hour.
- "Grasp the Nettle" is an old term meaning to approach a diffcult or problematic situation without hesitation.