A stinging plant or a plant with stinging hairs is a plant with hairs (

trichome Trichomes (); ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a pla ...

s) on its leaves or stems that are capable of injecting substances that cause pain or irritation. Other plants, such as

opuntia ''Opuntia'', commonly called prickly pear or pear cactus, is a genus of flowering plants in the cactus family Cactaceae. Prickly pears are also known as ''tuna'' (fruit), ''sabra'', ''nopal'' (paddle, plural ''nopales'') from the Nahuatl word f ...

s, have hairs or spines that cause mechanical irritation, but do not inject chemicals. Stinging hairs occur particularly in the

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...

Urticaceae, Loasaceae, Boraginaceae (subfamily Hydrophylloideae) and Euphorbiaceae. Such hairs have been shown to deter grazing mammals, but are no more effective against insect attack than non-stinging hairs. Many plants with stinging hairs have the word "nettle" in their English name, but may not be related to "true nettles" (the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

Urtica ''Urtica'' is a genus of flowering plants in the family Urticaceae. Many species have stinging hairs and may be called nettles or stinging nettles, although the latter name applies particularly to ''Urtica dioica''. ''Urtica'' species are food f ...

''). Though several unrelated families of plants have stinging hairs, their structure is generally similar. A solid base supports a single elongated cell with a brittle tip. When the tip is broken, the exposed sharp point penetrates the skin and pressure injects toxins. The precise chemicals involved in causing pain and irritation are not yet fully understood.

Structure and function of stinging hairs

Stiff hairs or

s without the ability to inject irritating compounds occur on the leaves and stems of many plants. They appear to deter feeding insects to some degree by impeding movement and restricting access to the surface of the stem or leaf. Some plants have glandular hairs, either as well as non-glandular hairs or instead of them. Glandular hairs have regions of tissue that produce secretions of secondary metabolites. These chemical substances can repel or poison feeding insects. Brennhaar-40x

Stinging hairs may be defined as those with ability to inject a chemical substance through the skin of an animal causing irritation or pain. Since some glandular hairs can cause irritation merely by contact, the difference between "stinging hairs" and "irritating hairs" is not always clear. For example, the hairs of ''

Mucuna ''Mucuna'' is a genus of around 100 accepted species of climbing lianas (vines) and shrubs of the family Fabaceae: tribe Phaseoleae, typically found in tropical forests. The leaves are trifoliolate, alternate, or spiraled, and the flowers are pe ...

'' species are described in both ways. Some species of ''Mucuna'' have sharply tipped hairs, in which the upper part easily breaks off, whereas other species have hairs that are blunter. In those subspecies of '' Urtica dioica'' that have stinging hairs (stinging nettles), these also have a point that easily breaks off, allowing the irritants in the cell below to enter through the skin. Being stung in this way has been shown to deter grazing mammals, such as rabbits, and even large herbivores such as cows. Many plant species respond to physical damage by producing a higher density of trichomes of all kinds. The general structure of a stinging hair is very similar in all the families of plants that possess them (except ''

Tragia ''Tragia'' is a genus of flowering plants in the spurge family, Euphorbiaceae. It is widespread across North and South America, Africa, the Arabian Peninsula, the Indian Subcontinent, northern Australia, and to various islands in the Caribbean ...

'' and ''

Dalechampia ''Dalechampia'' is a genus of plant of the family Euphorbiaceae and of the monogeneric subtribe Dalechampiinae. It is widespread across lowland tropical areas (generally below 2,000 m ASL) primarily in the Americas with smaller numbers of species ...

''). A multicellular base supports a single long thin cell, typically 1–8 mm long, with a brittle tip that easily breaks to form a sharp point that can penetrate skin. Stinging hairs of ''Urtica'' species have been studied in some detail. Each hair contains a fine tube, stiffened with calcium carbonate (calcified) at its base and with

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

(silicified) at its tip. In ''

Urtica thunbergiana ''Urtica thunbergiana'', also known as the Japanese nettle or hairy nettle, is a species of perennial herbs in the family Urticaceae. It is found in Japan, China and Taiwan. The habitat of the species is moist forests in the mountains. It is in ...

'', individual hairs contain around 4 nanolitres () of fluid. The silicified tip breaks off on contact, and the resulting fine point pierces the skin. Pressure forces the fluid out of the hair. Different toxins may be involved. The stinging hairs of ''

'' spp, notably ''

Tragia volubilis ''Tragia volubilis'' also known as fireman is a climbing subshrub or climbing shrub native to tropical America and Africa. It belongs to the Euphorbiaceae family, ''Tragia ''Tragia'' is a genus of flowering plants in the spurge family, Eup ...

'', a South American member of the Euphorbiaceae, are capable of injecting a crystal of

calcium oxalate Calcium oxalate (in archaic terminology, oxalate of lime) is a calcium salt of oxalic acid with the chemical formula . It forms hydrates , where ''n'' varies from 1 to 3. Anhydrous and all hydrated forms are colorless or white. The monohydrate ...

. The stinging sensation is initially caused by the mechanical entry of the stiff hair into the skin, but is then intensified by the effect of the oxalate. The effects of the stinging hairs of ''

'' species, particularly some subspecies of '' Urtica dioica'', have been attributed to a number of substances, including

histamine Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered in ...

acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Part ...

serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vas ...

, and

formic acid Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid, and has the chemical formula HCOOH and structure . It is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Es ...

. Histamine is a component of the stinging hairs of other ''Urtica'' species (e.g. '' U. urens'' and '' U. parviflora'') and of ''

Cnidoscolus urens ''Cnidoscolus urens'' is a perennial, tropical American stinging herb of the family Euphorbiaceae, and is one of some 100 species belonging to the genus ''Cnidoscolus'' (Gk. knidē-nettle, skōlos-thorn, Latin urens-burning). The plant is locally ...

'' and '' Laportea'' species. In

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

s, histamine is a

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neuro ...

. When it is released naturally, inflammation of the skin results, causing pain and itching. Injection of histamine by stinging hairs has been considered to have the same effect. This traditional interpretation was challenged in 2006 by research on ''Urtica thunbergiana'', the main species of ''Urtica'' present in

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...

. In tests on rats, the long-lasting pain caused by stings was attributed to oxalic and

tartaric acid Tartaric acid is a white, crystalline organic acid that occurs naturally in many fruits, most notably in grapes, but also in bananas, tamarinds, and citrus. Its salt, potassium bitartrate, commonly known as cream of tartar, develops naturally i ...

, although a synergistic effect of the other components of the stinging hairs was not ruled out. Fu et al. concluded that "stinging hairs, although studied for a long time, are still mysterious, particularly concerning the mechanism of the skin reaction after being stung."

Plants with stinging hairs

''Urtica''

Many plants with stinging hairs belong to the genus ''

''. Between twenty-four and thirty-nine species of flowering plants of the genus ''Urtica'' in the family Urticaceae fall into this category, with a

cosmopolitan Cosmopolitan may refer to: Food and drink * Cosmopolitan (cocktail), also known as a "Cosmo" History * Rootless cosmopolitan, a Soviet derogatory epithet during Joseph Stalin's anti-Semitic campaign of 1949–1953 Hotels and resorts * Cosmopoli ...

though mainly temperate distribution. They are mostly

herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition of t ...

perennial plant A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...

s, but some are annual and a few are

shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...

by. The most prominent member of the genus ''Urtica'' is the stinging nettle, ''Urtica dioica'', native to

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

, and

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

Other Urticaceae

The family Urticaceae also contains some other plants with stinging hairs that are not members of the genus ''Urtica''. These include: Gardenology

* '' Dendrocnide'' spp. ** '' Dendrocnide excelsa'' (giant stinging tree) ** '' Dendrocnide moroides'' (gympie-gympie) ** ''

Dendrocnide peltata ''Dendrocnide peltata'', commonly known simply as the stinging tree or ''jelaton'', is a large tree in the nettle family Urticaceae. With the other species of the genus ''Dendrocnide'', it is known for the stinging hairs which cover the whole p ...

'' (stinging tree, ''jelaton'') * ''

Girardinia diversifolia ''Girardinia diversifolia'', commonly known as the Himalayan nettle or Nilghiri nettle, is a plant species native to Nepal and in the Himalayan parts of India such as Uttarakhand, Himachal Pradesh and Jammu and Kashmir and in vast parts of China ...

'' (synonym: ''G. leschenaultiana'') (Nilgiri nettle, Himalayan giant nettle), source of allo fibre * '' Laportea canadensis'' (wood nettle) * ''

Urera ''Urera'' is a genus of flowering plants in the nettle family, Urticaceae. It has a pantropical distribution.Steinmann, V. W. (2005)Four new neotropical species and a new combination of ''Urera'' (Urticaceae).''Acta Botánica Mexicana'' (71), 19- ...

'' spp. ** '' Urera baccifera'' (nettle tree) ** '' Urera tenax''

Other families

There are also plants with stinging hairs that are unrelated to the Urticaceae: Cnidoscolus urens var

* Boraginaceae: Hydrophylloideae ** ''

Phacelia malvifolia ''Phacelia malvifolia'', with the common name stinging phacelia, is a species of phacelia. It is native plant, native to California, where it grows along the northern and Central Coast of California, central Coast and the California Coast Ranges. ...

'' (stinging phacelia) ** ''

Wigandia ''Wigandia'' is a genus of flowering plants within the waterleaf subfamily, Hydrophylloideae. They are found mainly in Central America and South America, though one or two species are found as far north as the United States. Some are grown as o ...

'' spp. * Euphorbiaceae ** ''

Cnidoscolus ''Cnidoscolus'' is a plant genus of the family Euphorbiaceae first described as a genus in 1827. The group is widespread across much of North and South America, including the West Indies. The name is derived from the Greek words κνίδη (''kn ...

'' spp. *** ''

Cnidoscolus stimulosus ''Cnidoscolus stimulosus'', the bull nettle, spurge nettle, tread-softly or finger rot, is a perennial herb covered with stinging hairs, native to southeastern North America. A member of the family Euphorbiaceae (spurge family), it is not a true ...

'' (bull nettle or spurge nettle) *** ''

'' (stinging spurge or mala mujer) ** '' Croton ciliato-glandulosus'' (ciega-vista) ** ''

'' spp. ** ''

'' spp. (noseburn) *

Fabaceae The Fabaceae or Leguminosae,International Code of Nomenc ...

** ''

'' spp. *** ''

Mucuna pruriens ''Mucuna pruriens'' is a tropical legume native to Africa and tropical Asia and widely naturalized and cultivated. Its English common names include monkey tamarind, velvet bean, Bengal velvet bean, Florida velvet bean, Mauritius velvet bean, Yo ...

'' (cowhage) * Loasaceae ** ''

Loasa ''Loasa'' is a genus of flowering plants in the family Loasaceae. The genus contains about 100 species native to Central and South America. Species of ''Loasa'' are prickly herbs or shrubs that have nettle-like stinging hairs. Some species of ...

'' spp. ** ''

Caiophora ''Caiophora'' is a genus of flowering plants belonging to the family Loasaceae. Its native range is Western and Southern South America to Southern Brazil. Species: *'' Caiophora aconquijae'' *''Caiophora andina'' *''Caiophora arechavaletae' ...

'' spp. ** ''

Cevallia ''Cevallia'' is a genus of flowering plants belonging to the family Loasaceae Loasaceae is a family of 15–20 genera and about 200–260 species of flowering plants in the order Cornales, native to the Americas and Africa. Members of the fa ...

'' spp. *

Solanaceae The Solanaceae , or nightshades, are a family of flowering plants that ranges from annual and perennial herbs to vines, lianas, epiphytes, shrubs, and trees, and includes a number of agricultural crops, medicinal plants, spices, weeds, and orn ...

** '' Solanum carolinense'' (Carolina horsenettle)

Toxicity

Though plants with stinging hairs can cause pain and acute urticaria, only a few are seriously harmful. The genus '' Dendrocnide'' (stinging trees) has been said to cause the most pain, particularly the Australian '' Dendrocnide moroides'' (gympie-gympie), although other sources describe the pain of stinging trees as only differing from that of nettles in terms of persistence rather than severity. There are reports of dogs and horses being killed, and once of a human death. The researcher Marina Hurley reports being hospitalized after being stung by a dead leaf. Deaths are probably due to heart failure caused by pain and shock. '' Urtica ferox'' (tree nettle or ongaonga) is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

. One recorded human death is known: a lightly clad young man died five hours after walking through a dense patch. After cooking, some plants with stinging hairs, such as '' Urtica dioica'' (stinging nettle), are eaten as vegetables.

References

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