Stinging nettle

''Urtica dioica'', often known as common nettle, burn nettle, stinging nettle (although not all plants of this species sting) or nettle leaf, or just a nettle or stinger, is a herbaceous perennial flowering plant in the family Urticaceae. Originally native to Europe, much of temperate Asia and western North Africa, it is now found worldwide, including New Zealand and North America. The species is divided into six subspecies, five of which have many hollow stinging hairs called trichomes on the leaves and stems, which act like hypodermic needles, injecting histamine and other chemicals that produce a stinging sensation upon contact ("contact urticaria", a form of contact dermatitis).

The plant has a long history of use as a source for traditional medicine, food, tea, and textile raw material in ancient (such as Saxon) and modern societies.

Description

''Urtica dioica'' is a dioecious, herbaceous, perennial plant, tall in the summer and dying down to the ground in winter. It has widely spreading rhizomes and stolons, which are bright yellow, as are the roots. The soft, green leaves are long and 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, numerous flowers in dense axillary inflorescences.

The leaves and stems are very hairy with non-stinging hairs, and in most subspecies, also bear many stinging hairs (trichomes or spicules), whose tips come off when touched, transforming the hair into a needle that can inject several chemicals causing a painful sting or paresthesia, giving the species its common names: stinging nettle, burn-nettle, burn-weed, or burn-hazel.

Taxonomy

The taxonomy of ''Urtica'' species 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, at least six clear subspecies of ''U. dioica'' are described, some formerly classified as separate species:
*''U. dioica'' subsp. ''dioica'' (European stinging nettle), from Europe, Asia, and northern Africa, has stinging hairs.
* ''U. dioica'' subsp. ''galeopsifolia'' (fen nettle or stingless nettle), from Europe, does not have stinging hairs.
*''U. dioica'' subsp. ''afghanica'', from southwestern and central Asia, sometimes has stinging hairs or is sometimes hairless.
*''U. dioica'' subsp. ''gansuensis'', from eastern Asia (China), has stinging hairs.
* ''U. dioica'' subsp. ''gracilis'' (Ait.) Selander (American stinging nettle), from North America, has stinging hairs and is monoecious.
*''U. dioica'' subsp. ''holosericea'' (Nutt.) Thorne (hoary stinging nettle), from North America, has stinging hairs and is monoecious.

Other species' names formerly accepted as distinct by some authors but now regarded as synonyms of one or other subspecies include ''U. breweri'', ''U. californica'', ''U. cardiophylla'', ''U. lyalli'', ''U. major'', ''U. procera'', ''U. serra'', ''U. strigosissima'', ''U. trachycarpa'', and ''U. viridis''.

Etymology

''Urtica'' is derived from a Latin word meaning 'sting'.Gledhill, David (2008). "The Names of Plants". Cambridge University Press. (hardback), (paperback). pp 142, 395

''Dioica'' (δίοικος) is derived from Greek, meaning 'of two houses' (having separate staminate and pistillate plants; dioecious).

Distribution and habitat

''U. dioica'' is considered to be native to Europe, much of temperate Asia and western North Africa. It is abundant in northern Europe and much of Asia, usually found in the countryside. It is less widespread in southern Europe and north Africa, where it is restricted by its need for moist soil, but is still common. It has been introduced to many other parts of the world. 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. It grows in abundance in the Pacific Northwest, especially in places where annual rainfall is high. The European subspecies has been introduced into Australia, North America and South America.

In Europe, nettles have a strong association with human habitation and buildings. The presence of nettles may indicate the site of a long-abandoned building, and can also indicate soil fertility. Human and animal waste may be responsible for elevated levels of phosphate and nitrogen in the soil, providing an ideal environment for nettles.

Ecology

Nettles are the larval food plant for several species of butterflies, such as the peacock butterfly, comma (''Polygonia c-album''), and the small tortoiseshell. It is 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'').

It is a known host to the pathogenic fungus ''Phoma herbarum''.Helgi Hallgrímsson & Guðríður Gyða Eyjólfsdóttir (2004)
''Íslenskt sveppatal I - smásveppir'' [Checklist of Icelandic Fungi I - Microfungi
Fjölrit Náttúrufræðistofnunar. Náttúrufræðistofnun Íslands [Icelandic Institute of Natural History]. ISSN 1027-832X

Stinging nettle is particularly found as an understory plant in wetter environments, but it is also found in meadows. Although nutritious, it is not widely eaten by either wildlife or livestock, presumably because of the sting. It spreads by abundant seeds and also by rhizomes, and is often able to survive and re-establish quickly after fire.

Cultivation

Field

Sowing and planting

Three cultivation techniques can be used for the stinging nettle: 1) direct sowing, 2) growing seedlings in nurseries with subsequent transplantation and 3) vegetative propagation via stolons or head cuttings.

# Direct sowing: The seedbed should have a loose and fine structure, but should be reconsolidated using a packer roller imminently prior to sowing. Sowing time can be either in autumn or in spring. Seed density should be 6 kilograms/hectare with row spacing of and 42–50 cm in autumn and spring, respectively. The disadvantage of direct sowing is that it usually leads to incomplete plant coverage. This drawback can be mitigated by covering the seedbed with a transparent perforated foil in order to improve seed germination. Further, weed control can be problematic as the stinging nettle has a slow seedling development time.
# Growing seedlings: For this technique pre-germinated seeds are sown between mid-/end-February and beginning of April and grown in nurseries. Seedlings are grown in tuffs with 3–5 plants/tuff and a seed density of 1.2–1.6 kg/1000 tuffs. A fastened germination is achieved by alternating high temperature during daytime (30 °C for 8 h) and lower temperature during nighttime (20 °C for 16 h). Before transplanting, the seedlings should be fertilized and acclimated to cold temperatures. Transplantation should start around Mid-April with row spacing of and plant spacing within rows of 25–30 cm.
# Vegetative propagation: Stolons (with several buds) of 10 cm should be planted from mid-April in a depth of . Head cuttings are grown in nurseries starting between mid-May and mid-June. Growing tips with two leaf pairs are cut from the mother plant and treated with root-growth inducing hormones. Transplantation can be delayed in comparison to the growing seedling technique.

Greenhouse

The stinging nettle can also be grown in controlled-environment agriculture systems, such as soil-less medium cultivations or aeroponics, which may achieve higher yields, standardize quality, and reduce harvesting costs and contamination.

Sting and treatment

''Urtica dioica'' produces its inflammatory effect on skin (stinging, burning sensation often called "contact urticaria") both by impaling the skin via spicules – causing mechanical irritation – and by biochemical irritants, such as histamine, serotonin, and acetylcholine, among other chemicals.Nettle (Stinging)
Wildflowerfinder.org.uk. Retrieved on 3 July 2012. Anti-itch drugs, usually in the form of creams containing antihistamines or hydrocortisone, may provide relief from nettle dermatitis. The term, ''contact urticaria'', has a wider use in dermatology, involving dermatitis caused by various skin irritants and pathogens.

Docks, especially the broad-leaf dock (''Rumex obtusifolius'') often grow in similar environments to stinging nettles and are regarded as a folk remedy to counteract the sting of a nettle, although there is no evidence of any chemical effect. It may be that the act of rubbing a dock leaf against a nettle sting acts as a distracting counterstimulation, or that belief in the dock's effect provides a placebo effect.

Uses

Culinary

''U. dioica'' has a flavour similar to spinach when cooked. Young plants were harvested by Native Americans and used as a cooked plant in spring when other food plants were scarce.Gregory L. Tilford, ''Edible and Medicinal Plants of the West'', Soaking stinging nettles in water or cooking removes the stinging chemicals from the plant, which allows them to be handled and eaten without injury. After the stinging nettle enters its flowering and seed-setting stages, the leaves develop gritty particles called cystoliths, which can irritate the kidneys and urinary tract. Cystoliths are made of calcium carbonate, and will not dissolve when boiled. Leaves harvested post-flowering must have their cystoliths broken down by acid, as in the fermentation process. In its peak season, nettle contains up to 25% protein, dry weight, which is high for a leafy green vegetable. The leaves are also dried and may then be used to make a herbal tea, as can also be done with the nettle's flowers.

Nettles can be used in a variety of recipes, such as polenta, pesto, and purée. Nettle soup is a common use of the plant, particularly in Northern and Eastern Europe.

Nettles are sometimes used in cheesemaking, such as for Cornish Yarg and as a flavouring in varieties of Gouda.

Nettles are used in Montenegro, Serbia, and Bosnia and Hercegovina as part of the dough filling for the ''börek'' pastry. The top baby leaves are selected and simmered, and then mixed with other ingredients such as herbs and rice, before being used as a filling between dough layers. Similarly, in Greece the tender leaves are often used, after simmering, as a filling for hortopita, which is similar to spanakopita, but with wild greens rather than spinach for filling.

Young nettles can also be used to make an alcoholic drink.

Competitive eating

In the UK, an annual World Nettle Eating Championship draws thousands of people to Dorset, where competitors attempt to eat as much of the raw plant as possible. Competitors are given stalks of the plant, from which they strip the leaves and eat them. Whoever strips and eats the most stinging nettle leaves in a fixed time is the winner. The competition dates back to 1986, when two neighbouring farmers attempted to settle a dispute about which had the worst infestation of nettles, and one of them said, "I'll eat any nettle of yours that's longer than mine."

Traditional medicine

As Old English ''stiðe'', nettle is one of the nine plants invoked in the pagan Anglo-Saxon ''Nine Herbs Charm'', recorded in 10th-century traditional medicine. Nettle was believed to be a galactagogue – a substance that promotes lactation. Urtication, or flogging with nettles is the process of deliberately applying stinging nettles to the skin to provoke inflammation. An agent thus used was considered to be a rubefacient (something that causes redness), used as a folk remedy for treating rheumatism.

Chastisement

In indigenous justice systems in Ecuador, urtication was used as punishment for severe crimes in 2010. The sentenced perpetrator of a crime was flogged with stinging nettle, in public, naked, whilst being showered with freezing cold water.

Textiles and fibre

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.

Historically, nettles have been used to make clothing for almost 3,000 years, as ancient nettle textiles from the Bronze Age have been found in Denmark. It is widely believed that German Army uniforms were almost all made from nettle during World War I due to a potential shortage of cotton, although there is little evidence to support this. More recently, companies in Austria, Germany, and Italy have started to produce commercial nettle textiles.

The fibre content in nettle shows a high variability and reaches from below 1% to 17%. Under middle-European conditions, stems yield typically between 45 and 55 dt / ha (decitons per hectare), which is comparable to flax stem yield. Due to the variable fibre content, the fibre yields vary between 0.2 and 7 dt / ha, but the yields are normally in the range between 2 and 4 dt / ha. Fibre varieties are normally cloning varieties and therefore planted from vegetative propagated plantlets. Direct seeding is possible, but leads to great heterogeneity in maturity.

Nettles may be used as a dye-stuff, producing yellow from the roots, or yellowish green from the leaves.

Feed

Nutrient contents

Fresh leaves contain approximately 82.4% water, 17.6% dry matter, 5.5% protein, 0.7 to 3.3% fat, and 7.1% carbohydrates. Mature leaves contain about 40% '' α'' - linolenic acid, a valuable omega-3 acid. For exact fatty acid contents see Table 1. Seeds contain much more fatty acid than leaves.

Minerals (Ca, K, Mg, P, Si, S, Cl) and trace elements ( Ti, 80 ppm, Mn, Cu, Fe) contents depend mostly on the soil and the season.

Carotenoids can be found primarily in the leaves, where different forms of lutein