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''Mentha pulegium'', commonly (European) pennyroyal, or pennyrile, also called mosquito plant and pudding grass, is a
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
of
flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. They include all forbs (flowering plants without a woody stem), grasses and grass-like plants, a vast majority of ...
in the mint
family 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. Idea ...
,
Lamiaceae The Lamiaceae ( ) or Labiatae are a family of flowering plants commonly known as the mint, deadnettle or sage family. Many of the plants are aromatic in all parts and include widely used culinary herbs like basil, mint, rosemary, sage, savo ...
, 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 subcontinent of Eurasia and it is located enti ...
,
North Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in t ...
, and the
Middle East The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabia (including the Arabian Peninsula and Bahrain), Asia Minor (Asian part of Turkey except Hatay Province), East Thrace (Europ ...
. Crushed pennyroyal leaves emit a very strong fragrance similar to spearmint. Pennyroyal is a traditional folk remedy, emmenagogue,
abortifacient An abortifacient ("that which will cause a miscarriage" from Latin: '' abortus'' "miscarriage" and '' faciens'' "making") is a substance that induces abortion. This is a nonspecific term which may refer to any number of substances or medications ...
, and culinary herb, but is toxic to the liver and has caused some deaths. European pennyroyal is related to an American species,
Hedeoma pulegioides ''Hedeoma pulegioides'', the American pennyroyal or American false pennyroyal,USDA Plants Profile''Hedeoma pulegioides'' Accessed June 19, 2007. is a species of ''Hedeoma'' native to eastern North America, from Nova Scotia and southern Ontario w ...
. Though they differ in
genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...
, they share similar chemical properties.


Description

An annual to perennial plant with creeping or erect branched stems to about 40 cm in height. The stems are square in cross-section and can vary from hairless on some plants to densely hairy on others, with a green to sometimes red or purplish colour. The leaves, which grow in opposite pairs, are narrowly oval, 2–3 cm long x 1 cm wide, downy, sparsely toothed towards the tip, and taper into a short
stalk Stalk or stalking may refer to: Behaviour * Stalk, the stealthy approach (phase) of a predator towards its prey * Stalking, an act of intrusive behaviour or unwanted attention towards a person * Deer stalking, the pursuit of deer for sport Biol ...
. All parts of the plant are strongly scented when crushed but it does not have noticeable glands on its surface. The small (6 mm) flowers are densely packed in whorls at the nodes, widely separated, above pairs of leaf-like bracts. The
calyx Calyx or calyce (plural "calyces"), from the Latin ''calix'' which itself comes from the Ancient Greek ''κάλυξ'' (''kálux'') meaning "husk" or "pod", may refer to: Biology * Calyx (anatomy), collective name for several cup-like structures ...
is a ribbed tube about 3 mm long, with 5 triangular teeth, the lower 2 being narrower and slightly longer than the upper 3; it is hairy both on the inside and the outside. The
corolla Corolla may refer to: *Corolla (botany), the petals of a flower, considered as a unit *Toyota Corolla, an automobile model name * Corolla (headgear), an ancient headdress in the form of a circlet or crown * ''Corolla'' (gastropod), a genus of moll ...
has 4 mauve lobes or "petals" and is hairy only on the outside. The flowers are
bisexual Bisexuality is a romantic or sexual attraction or behavior toward both males and females, or to more than one gender. It may also be defined to include romantic or sexual attraction to people regardless of their sex or gender identity, wh ...
and have 4 long
stamens The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filam ...
, 2 (or all 4) of which project well beyond the corolla lobes. There is one long style which is forked to produce 2 stigmas, which also project from the flower. The fruits consist of a cluster of four brown, 1-seeded nutlets, each about 0.7 mm long. The flowering period starts in June and continues into mid-summer, although in northern countries it flowers rather later, sometimes as late as September, when it can fail to set seed. Its chromosome number is 2n = 20.


Distribution

The native range of pennyroyal is thought to be around the eastern
Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on th ...
, where it grows in damp meadows, around pools and in stream margins. It is, however, very widely established around the world, including North and South America, throughout Africa, Asia, Australia and New Zealand. In many places it is considered a troublesome weed of agriculture. Towards the northern edge of its range, as in Britain, it is considered to be rare and declining, except where introduced.


Habitat and ecology

The habitat of pennyroyal is seasonally damp pasture, where standing water over the winter leaves bare ground in the summer, and where livestock preferentially graze other plants. An analogue of this habitat is found on roadsides, where trampling or disturbance of the ground produces similarly bare soil, particularly where there is waterlogging in winter. It is also found along watercourses, in wet woodland and in abandoned fields. In California, where it is considered an invasive species, it occupies a similar niche, in seeps, streamsides, vernal pools and swales, marshes, and ditches. There is some speculation that it may displace native species in these areas. Few animals eat pennyroyal. In Britain, the only insect known to feed on it is the bug '' Heterogaster artemisiae'' Schilling, which is a seed bug that normally feeds on
wild thyme ''Thymus serpyllum'', known by the common names of Breckland thyme, Breckland wild thyme, wild thyme, creeping thyme, or elfin thyme, is a species of flowering plant in the mint family Lamiaceae, native to most of Europe and North Africa. I ...
. It is considered an
axiophyte An axiophyte (Greek: "worthy plant") is a plant that is of particular interest to botanists, conservationists and ecologists. The significance of axiophytes is from their strong association with habitats considered to be of high merit for conserva ...
in many British counties, because low-intensity pasture is a rare habitat, although it has been spreading in recent decades. Its Ellenberg values in Britain are L = 8, F = 7, R = 5, N = 7, and S = 0.


History


Ancient to modern use

Documented use of pennyroyal dates back to ancient
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
, Roman, and
Medieval In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire a ...
cultures. Its name – although of uncertain etymology – is associated with Latin ''pulex'' (flea), alluding to the manner it was used to drive away fleas when smeared on the body. Pennyroyal was commonly incorporated as a cooking
herb In general use, herbs are a widely distributed and widespread group of plants, excluding vegetables and other plants consumed for macronutrients, with savory or aromatic properties that are used for flavoring and garnishing food, for medicina ...
by the
Greeks The Greeks or Hellenes (; el, Έλληνες, ''Éllines'' ) are an ethnic group and nation indigenous to the Eastern Mediterranean and the Black Sea regions, namely Greece, Greek Cypriots, Cyprus, Greeks in Albania, Albania, Greeks in Italy, ...
and Romans. A large number of the recipes in the Roman cookbook of
Apicius ''Apicius'', also known as ''De re culinaria'' or ''De re coquinaria'' (''On the Subject of Cooking'') is a collection of Roman cookery recipes. It is thought to have been compiled in the fifth century AD. Its language is in many ways close ...
called for the use of pennyroyal, often along with such herbs as lovage, oregano and
coriander Coriander (;
. Although it was commonly used for cooking also in the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
, it gradually fell out of use as a culinary herb and is seldom used as such today. Records from Greek and Roman physicians and scholars contain information pertaining to pennyroyal's medicinal properties, as well as recipes used to prepared it.
Pliny the Elder Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, naturalist and natural philosopher, and naval and army commander of the early Roman Empire, and a friend of the emperor Vespasian. He wrote the encyclopedic ...
, in his encyclopedia ''
Naturalis Historia The ''Natural History'' ( la, Naturalis historia) is a work by Pliny the Elder. The largest single work to have survived from the Roman Empire to the modern day, the ''Natural History'' compiles information gleaned from other ancient authors. ...
'' (''Natural History''), described the plant as an emmenagogue, and that it also expelled a dead
fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal develo ...
.
Galen Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized as Galen () or Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be on ...
only listed pennyroyal as an emmenagogue, as did Oribasius. Roman and Greek writers Quintus Serenus Sammonicus and Aspasia the Physician however both agreed that pennyroyal, when served in tepid water, was an effective abortive method. A medical text on
gynecology Gynaecology or gynecology (see spelling differences) is the area of medicine that involves the treatment of women's diseases, especially those of the reproductive organs. It is often paired with the field of obstetrics, forming the combined ar ...
attributed to
Cleopatra Cleopatra VII Philopator ( grc-gre, Κλεοπάτρα Φιλοπάτωρ}, "Cleopatra the father-beloved"; 69 BC10 August 30 BC) was Queen of the Ptolemaic Kingdom of Ancient Egypt, Egypt from 51 to 30 BC, and its last active ruler. ...
(though it was actually written by a female Greek physician Metrodora) recommends the use of pennyroyal with wine to induce abortions. In regard to its contraceptive properties, it was referred to in a joking manner in
Aristophanes Aristophanes (; grc, Ἀριστοφάνης, ; c. 446 – c. 386 BC), son of Philippus, of the deme Kydathenaion ( la, Cydathenaeum), was a comic playwright or comedy-writer of ancient Athens and a poet of Old Attic Comedy. Eleven of his fo ...
' play ''
Peace Peace is a concept of societal friendship and harmony in the absence of hostility and violence. In a social sense, peace is commonly used to mean a lack of conflict (such as war) and freedom from fear of violence between individuals or groups. ...
'' (421 BCE). The god
Hermes Hermes (; grc-gre, Ἑρμῆς) is an Olympian deity in ancient Greek religion and mythology. Hermes is considered the herald of the gods. He is also considered the protector of human heralds, travellers, thieves, merchants, and orato ...
provides the male character Trygaios a female companion; when Trygaios asks if there would be a problem if she became pregnant, Hermes responds, "Not if you add a dose of pennyroyal." In a similar manner, in Aristophanes' comedy ''
Lysistrata ''Lysistrata'' ( or ; Attic Greek: , ''Lysistrátē'', "Army Disbander") is an ancient Greek comedy by Aristophanes, originally performed in classical Athens in 411 BC. It is a comic account of a woman's extraordinary mission to end the Peloponne ...
'', after a pregnant female character on stage is told to withhold her body sexually from her husband, a slender female character, in comparison to the pregnant woman, is described as "a very lovely land Well croppy, and trimmed and spruced with pennyroyal." Early settlers in colonial Virginia used dried pennyroyal to eradicate pests. Pennyroyal was such a popular herb that the
Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, r ...
published an article on its use against rattlesnakes in the first volume of its
Philosophical Transactions ''Philosophical Transactions of the Royal Society'' is a scientific journal published by the Royal Society. In its earliest days, it was a private venture of the Royal Society's secretary. It was established in 1665, making it the first journa ...
in 1665. 17th century apothecary and physician
Nicholas Culpeper Nicholas Culpeper (18 October 1616 – 10 January 1654) was an English botanist, herbalist, physician and astrologer.Patrick Curry: "Culpeper, Nicholas (1616–1654)", ''Oxford Dictionary of National Biography'' (Oxford, UK: OUP, 2004) His bo ...
mentioned pennyroyal in his medical text '' The English Physitian'', published in 1652. In addition to its abortive properties, Culpeper recommends its use for
gastrointestinal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...
ailments, such as
constipation Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bowel moveme ...
and
hemorrhoids Hemorrhoids (or haemorrhoids), also known as piles, are vascular structures in the anal canal. In their normal state, they are cushions that help with stool control. They become a disease when swollen or inflamed; the unqualified term '' ...
, as well as itching and blemishes to the skin, and even toothaches. Pennyroyal is an essential ingredient in the North african dish, which is still eaten to the this day, called . Pennyroyal continued to be used up through the 20th and 21st centuries. Its oil is still commercially available today, though little is known about the appropriate dosages for humans. Scientists therefore likely consider it unsafe for use, as it is potentially toxic.


Uses

Pennyroyal is frequently used as an insecticide and pest repellent. As a pest repellent, it is used to keep fleas away from household animals as well as on humans to ward off gnats and mosquitos. Some flea collars for pets have pennyroyal oil or the herb can be crushed in the lining. Humans have also put crushed pennyroyal stems in their pockets or on their clothing to ward off unwanted insects. However, when using the pennyroyal plant as a pest repellent, the use of the concentrated pennyroyal oil should be avoided. Pennyroyal oil can be extremely toxic to both humans and animals, even in small quantities. With the use of pennyroyal around animals and humans comes the risk of it being absorbed through the skin and causing negative health effects. The less concentrated leaves of the plant should be used instead as an insect repellent. Pennyroyal has historically also been used as a mint flavoring in herbal teas and foods. Pennyroyal tea has been used for cold relief, fevers, coughs, indigestion, liver and kidney problems and headaches. The fresh or dried leaves of pennyroyal have also been used when treating influenza, abdominal cramps, to induce sweating, as well as in the treatment of diseases such as smallpox and tuberculosis. To make the tea, the leaves of the plant are boiled in hot water. The lower concentrations of toxic chemicals in these teas are less harmful than pennyroyal oil. It is recommended that people only drink pennyroyal tea periodically, as it is taxing on the body and should not be drunk on a regular basis. Consumption of pennyroyal tea can be fatal to infants and children. In Italy the fresh leaves of this plant, which in Rome and the surrounding area is called ''menta romana'', are used in the capital's cuisine to flavour lamb and
tripe Tripe is a type of edible lining from the stomachs of various farm animals. Most tripe is from cattle, pigs and sheep. Types of tripe Beef tripe Beef tripe is made from the muscle wall (the interior mucosal lining is removed) of a cow' ...
. In culinary use it should not be confused with lesser calamint (''Clinopodium nepeta''), which in Rome is used to prepare
artichoke The globe artichoke ('' Cynara cardunculus'' var. ''scolymus'' ),Rottenberg, A., and D. Zohary, 1996: "The wild ancestry of the cultivated artichoke." Genet. Res. Crop Evol. 43, 53–58. also known by the names French artichoke and green artich ...
s. The pennyroyal plant has also been used as an emmenagogue or perhaps most famously as an
abortifacient An abortifacient ("that which will cause a miscarriage" from Latin: '' abortus'' "miscarriage" and '' faciens'' "making") is a substance that induces abortion. This is a nonspecific term which may refer to any number of substances or medications ...
. Chemicals in the pennyroyal plant cause the uterine lining to contract, causing a woman's uterine lining to shed. Women who struggle with regulating their menstrual cycle or suffer from a cystic ovary syndrome may choose to drink pennyroyal tea. Pennyroyal tea is subtle enough to induce menstrual flow with minimal risk of negative health effects. More concentrated versions of the plant, such as the oil, are much more toxic and will likely force a miscarriage if ingested by a pregnant woman. Since the U.S. Congress passed the Dietary Supplement Health and Education Act in October 1994 all manufactured forms of pennyroyal in the United States have carried a warning label against its use by pregnant women, but pennyroyal is not regulated by the U.S. Food and Drug Administration. Rennie's 1833 supplement to the pharmacopeias admitted its use as an "expectorant, diuretic, and emmenagogue" in doses of 10 grains to 1 scruple (0.6–1.3g) of the powdered dried herb, but dismissed the use of the Pennyroyal Water (Aqua Pulegii) as "popularly but erroneously supposed" to be an abortifacient o mention is made of toxicity At least one study has shown pennyroyal oil to have potent
acaricidal Acaricides are pesticides that kill members of the arachnid subclass ''Acari'', which includes ticks and mites. Acaricides are used both in medicine and agriculture, although the desired selective toxicity differs between the two fields. Termino ...
activity against house dust mites.


Toxicity

Pennyroyal is toxic to humans and has differing effects dependent on the volume and concentration ingested. The most concentrated and toxic form of the pennyroyal plant is pennyroyal oil. The oil contains 80% to 92% of cyclohexanone pulegone. Pulegone, the molecule in highest concentration in the pennyroyal plant, causes a variety of ailments in those who ingest it and is what causes the plant to have its peppermint flavor. Symptoms that may persist after ingesting a small dose (<10 mL) of pennyroyal oil are nausea, vomiting, abdominal pain and dizziness. Larger volumes may result in multiorgan failure that could lead to death. There are no current toxicokinetics studies performed on humans for the effects of pulegone, but there are some studies performed on other mammals. When pulegone is ingested, it is broken down by the liver and reacts to form multiple toxic metabolites that can wreak havoc in the body. Some identified metabolites are
menthofuran Menthofuran is an organic compound found in a variety of essential oils including that of pennyroyal (''Mentha pulegium''). It is highly toxic and believed to be the primary toxin in pennyroyal responsible for its potentially fatal effects. Aft ...
, piperitenone, piperitone, and menthone.


Chemistry


Structure and reactivity

The active chemical in pennyroyal is pulegone. Pulegone is a
ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bon ...
and on the cellular level, ketones can act as
enzyme inhibitor An enzyme inhibitor is a molecule that binds to an enzyme and blocks its activity. Enzymes are proteins that speed up chemical reactions necessary for life, in which substrate molecules are converted into products. An enzyme facilitates a s ...
s. The carbonyl center of the pulegone structure acts as a strong electrophile, causing active sites on enzymes to bind with pulegone instead of the target protein. The exocyclic
double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...
found in pulegone is vital to the activation and binding mechanism of the molecule and causes it to be an effective hepatotoxin. When ingested, pulegone targets the liver and kidney, among other organs. Studies have been conducted on rats show that one of the main effects is the inhibition of contractile activity in the myometrium and death by kidney failure. Also found in the study, long term exposure to pennyroyal increased incidences of urinary bladder tumors.


Mechanism of action

The exact mechanism of action by which pennyroyal induces menses and
abortion Abortion is the termination of a pregnancy by removal or expulsion of an embryo or fetus. An abortion that occurs without intervention is known as a miscarriage or "spontaneous abortion"; these occur in approximately 30% to 40% of pregn ...
s in humans is still unknown. Studies using animal models speculate the source of liver toxicity is due to one of the many constituents the plant contains: pulegone, a monoterpene. Pulegone is metabolized by
cytochrome P450 Cytochromes P450 (CYPs) are a superfamily of enzymes containing heme as a cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are important for the clearance of various compo ...
(CYP 1A2 and 2E1) and converted to several toxins. Both ''
in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology and ...
'' and ''
in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...
'' studies have found the pulegone metabolite
menthofuran Menthofuran is an organic compound found in a variety of essential oils including that of pennyroyal (''Mentha pulegium''). It is highly toxic and believed to be the primary toxin in pennyroyal responsible for its potentially fatal effects. Aft ...
to be an inhibitor of
CYP2A6 Cytochrome P450 2A6 (abbreviated CYP2A6) is a member of the cytochrome P450 mixed-function oxidase system, which is involved in the metabolism of xenobiotics in the body. CYP2A6 is the primary enzyme responsible for the oxidation of nicotine and ...
, accounting for a significant degree of pennyroyal's
hepatotoxicity Hepatotoxicity (from ''hepatic toxicity'') implies chemical-driven liver damage. Drug-induced liver injury is a cause of acute and chronic liver disease caused specifically by medications and the most common reason for a drug to be withdrawn fr ...
. The exact pathway pulegone undergoes to be converted to menthofuran is unknown, but one study strongly suggested it included allylic oxidation of a methyl group (from CYP450), intramolecular cyclization to form a hemiketal, and subsequent dehydration to form the furan. Additionally, pulegone and menthofuran may deplete glutathione levels, leaving hepatocytes vulnerable to free radical damage.


Treatment

There is no known antidote for pennyroyal toxicity. Case studies involving pennyroyal poisonings have reported the use of gastric lavages and administration of emetics or
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenteri ...
inducing agents, or absorbents like activated charcoal. As
glutathione Glutathione (GSH, ) is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals, pe ...
depletion has been shown to regulate liver toxification, administration of N-acetylcysteine in similar doses as given for acetaminophen toxicity have been given to patients. A study testing pulegone toxicity found inhibitors of cytochrome P450, such as
cobaltous chloride Cobalt(II) chloride is an inorganic compound of cobalt and chlorine, with the formula . The compound forms several hydrates ·''n'', for ''n'' = 1, 2, 6, and 9. Claims of the formation of tri- and tetrahydrates have not been confirmed.M. T. Saugi ...
or piperonyl butoxide, blocked toxicity. Such testing has not been expanded to humans, however, as the pennyroyal mechanism of toxicity is still not entirely understood.


See also

* ''
Hedeoma pulegioides ''Hedeoma pulegioides'', the American pennyroyal or American false pennyroyal,USDA Plants Profile''Hedeoma pulegioides'' Accessed June 19, 2007. is a species of ''Hedeoma'' native to eastern North America, from Nova Scotia and southern Ontario w ...
'' (American pennyroyal, a distantly related species)


References


External links

*ARKive
images and movies of the Pennyroyal ''(Mentha pulegium)''
{{Taxonbar, from=Q161235 Abortifacients pulegium Medicinal plants Herbs Flora of Europe Flora of North Africa Plants described in 1753 Taxa named by Carl Linnaeus