Poison ivy
Overview
Toxicodendron radicans, better known as poison ivy (older synonyms are Rhus toxicodendron and Rhus radicans), is a poisonous North American plant that is well known for its production of urushiol
Urushiol
Urushiol is an oily organic allergen found in plants of the family Anacardiaceae, especially Toxicodendron spp. . It causes an allergic skin rash on contact, known as urushiol-induced contact dermatitis...

, a clear liquid compound found within the sap
Sap
Sap may refer to:* Plant sap, the fluid transported in xylem cells or phloem sieve tube elements of a plant* Sap , a village in the Dunajská Streda District of Slovakia...

 of the plant that causes an itching rash
Urushiol-induced contact dermatitis
Urushiol-induced contact dermatitis is the medical name given to allergic rashes produced by the oil urushiol, which is contained in various plants, including the plants of the genus Toxicodendron , other plants in the family Anacardiaceae Urushiol-induced contact dermatitis (also called...

 in most people who touch it. The plant is not a true ivy
Ivy
Ivy, plural ivies is a genus of 12–15 species of evergreen climbing or ground-creeping woody plants in the family Araliaceae, native to western, central and southern Europe, Macaronesia, northwestern Africa and across central-southern Asia east to Japan and Taiwan.-Description:On level ground they...

 (Hedera).

Poison ivy can be found growing in any of the following three forms:
  • as a trailing vine that is 10–25 cm tall (4 to 10 inches)
  • as a shrub
    Shrub
    A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...

     up to 1.2 m tall (4 feet)
  • as a climbing vine that grows on trees or some other support

Poison ivy grows throughout much of North America, including the Canadian Maritime provinces, Quebec, Ontario, Manitoba, and all U.S.
Discussions
Encyclopedia
Toxicodendron radicans, better known as poison ivy (older synonyms are Rhus toxicodendron and Rhus radicans), is a poisonous North American plant that is well known for its production of urushiol
Urushiol
Urushiol is an oily organic allergen found in plants of the family Anacardiaceae, especially Toxicodendron spp. . It causes an allergic skin rash on contact, known as urushiol-induced contact dermatitis...

, a clear liquid compound found within the sap
Sap
Sap may refer to:* Plant sap, the fluid transported in xylem cells or phloem sieve tube elements of a plant* Sap , a village in the Dunajská Streda District of Slovakia...

 of the plant that causes an itching rash
Urushiol-induced contact dermatitis
Urushiol-induced contact dermatitis is the medical name given to allergic rashes produced by the oil urushiol, which is contained in various plants, including the plants of the genus Toxicodendron , other plants in the family Anacardiaceae Urushiol-induced contact dermatitis (also called...

 in most people who touch it. The plant is not a true ivy
Ivy
Ivy, plural ivies is a genus of 12–15 species of evergreen climbing or ground-creeping woody plants in the family Araliaceae, native to western, central and southern Europe, Macaronesia, northwestern Africa and across central-southern Asia east to Japan and Taiwan.-Description:On level ground they...

 (Hedera).

Poison ivy can be found growing in any of the following three forms:
  • as a trailing vine that is 10–25 cm tall (4 to 10 inches)
  • as a shrub
    Shrub
    A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...

     up to 1.2 m tall (4 feet)
  • as a climbing vine that grows on trees or some other support

Distribution and habitat

Poison ivy grows throughout much of North America, including the Canadian Maritime provinces, Quebec, Ontario, Manitoba, and all U.S. states east of the Rockies, as well as in the mountainous areas of Mexico up to around 1500 m (4,921.3 ft) (caquistle or caxuistle is the Nahuatl
Nahuatl
Nahuatl is thought to mean "a good, clear sound" This language name has several spellings, among them náhuatl , Naoatl, Nauatl, Nahuatl, Nawatl. In a back formation from the name of the language, the ethnic group of Nahuatl speakers are called Nahua...

 term), and is normally found in wooded areas, especially along edge areas. It also grows in exposed rocky areas and in open fields and disturbed areas. It can grow as a forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...

 understory
Understory
Understory is the term for the area of a forest which grows at the lowest height level below the forest canopy. Plants in the understory consist of a mixture of seedlings and saplings of canopy trees together with understory shrubs and herbs...

 plant, although it is only somewhat shade tolerant. The plant is extremely common in suburban and exurban areas of New England, the Mid-Atlantic, and southeastern United States. Similar species, poison oak, and Toxicodendron rydbergii are found in western North America. Poison ivy rarely grows at altitudes above 1500 m (4,921.3 ft), although the altitude limit varies in different locations. The plants can grow as a shrub up to about 1.2 metres (3.9 ft) tall, as a groundcover
Groundcover
Groundcover refers to any plant that grows over an area of ground, used to provide protection from erosion and drought, and to improve its aesthetic appearance .- Ecosystem :...

 10–25 cm (3.9–9.8 in) high, or as a climbing vine on various supports. Older vines on substantial supports send out lateral branches that may at first be mistaken for tree limbs.

It is not particularly sensitive to soil moisture, although it does not grow in desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...

 or arid
Arid
A region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life...

 conditions. It grows in a wide variety of soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

 types, and soil pH
Soil pH
The soil pH is a measure of the acidity or basicity in soils. pH is defined as the negative logarithm of the activity of hydrogen ions in solution. It ranges from 0 to 14, with 7 being neutral. A pH below 7 is acidic and above 7 is basic. Soil pH is considered a master variable in soils as it...

 from 6.0 (acidic) to 7.9 (moderately alkaline). It can grow in areas subject to seasonal flooding or brackish water.

It is more common now than when Europeans
European colonization of the Americas
The start of the European colonization of the Americas is typically dated to 1492. The first Europeans to reach the Americas were the Vikings during the 11th century, who established several colonies in Greenland and one short-lived settlement in present day Newfoundland...

 first entered North America. Real estate development adjacent to wild, undeveloped land has engendered "edge effect
Edge effect
The edge effect in ecology is the effect of the juxtaposition or placing side by side of contrasting environments on an ecosystem.This term is commonly used in conjunction with the boundary between natural habitats, especially forests, and disturbed or developed land. Edge effects are especially...

s," enabling poison ivy to form vast, lush colonies in such places. It is listed as a noxious weed in the U.S. states of Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...

 and Michigan
Michigan
Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....

 and the Canadian province of Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....

.

Poison ivy and its relatives are virtually unknown in Europe.

Description

The deciduous
Deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...

 leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

 of poison ivy are trifoliate
Leaf shape
In botany, leaf shape is characterised with the following terms :* Acicular : Slender and pointed, needle-like* Acuminate : Tapering to a long point...

 with three almond
Almond
The almond , is a species of tree native to the Middle East and South Asia. Almond is also the name of the edible and widely cultivated seed of this tree...

-shaped leaflet
Leaflet
A leaflet in botany is a part of a compound leaf. A leaflet may resemble an entire leaf, but it is not borne on a stem as a leaf is, but rather on a vein of the whole leaf. Compound leaves are common in many plant families...

s. Leaf colour ranges from light green (usually the younger leaves) to dark green (mature leaves), turning bright red in fall
Autumn
Autumn is one of the four temperate seasons. Autumn marks the transition from summer into winter usually in September or March when the arrival of night becomes noticeably earlier....

; though other sources say leaves are reddish when expanding, turn green through maturity, then back to red, orange, or yellow in the fall. The leaflets of mature leaves are somewhat shiny. The leaflets are 3 to 12 cm (1.2 to 4.7 in) long, rarely up to 30 cm (11.8 in). Each leaflet has a few or no teeth along its edge, and the leaf surface is smooth. Leaflet clusters are alternate on the vine, and the plant has no thorns. Vines growing on the trunk of a tree become firmly attached through numerous aerial rootlets. The vines develop adventitious roots, or the plant can spread from rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s or root crown
Crown sprouting
Crown sprouting is the ability of a plant to regenerate its shoot system after destruction by activating dormant vegetative structures to produce regrowth from the root crown . These dormant structures take the form of lignotubers or basal epicormic buds...

s. The milky sap of poison ivy darkens after exposure to the air.

Poison ivy spreads either vegetatively
Vegetative reproduction
Vegetative reproduction is a form of asexual reproduction in plants. It is a process by which new individuals arise without production of seeds or spores...

 or sexually
Plant sexuality
Plant sexuality covers the wide variety of sexual reproduction systems found across the plant kingdom. This article describes morphological aspects of sexual reproduction of plants....

. Poison ivy is dioecious; flowering occurs from May to July. The yellowish- or greenish-white flowers are typically inconspicuous and are located in clusters up to 8 cm (3.1 in) above the leaves. The berry-like fruit, a drupe
Drupe
In botany, a drupe is a fruit in which an outer fleshy part surrounds a shell of hardened endocarp with a seed inside. These fruits develop from a single carpel, and mostly from flowers with superior ovaries...

, mature by August to November with a grayish-white colour. Fruits are a favourite winter food of some birds and other animals. Seeds are spread mainly by animals and remain viable after passing through the digestive tract.

Aids to identification

The following four characteristics are sufficient to identify poison ivy in most situations: (a) clusters of three leaflets, (b) alternate leaf arrangement, (c) lack of thorns, and (d) each group of three leaflets grows on its own stem, which connects to the main vine.

The appearance of poison ivy can vary greatly between environments, and even within a single area. Identification by experienced people is often made difficult by leaf damage, the plant's leafless condition during winter, and unusual growth forms due to environmental or genetic factors.

Various mnemonic
Mnemonic
A mnemonic , or mnemonic device, is any learning technique that aids memory. To improve long term memory, mnemonic systems are used to make memorization easier. Commonly encountered mnemonics are often verbal, such as a very short poem or a special word used to help a person remember something,...

 rhymes describe the characteristic appearance of poison ivy:
  1. "Longer middle stem; stay away from them." This refers to the middle leaflet having a visibly longer stem than the two side leaflets and is a key to differentiating it from the similar-looking Rhus aromatica
    Rhus aromatica
    Rhus aromatica is a plant species in the family Anacardiaceae native to Canada and the United States....

    (fragrant sumac).
  2. "Leaves of three; let it be."
  3. "Hairy vine, no friend of mine." Poison ivy vines are very poisonous.
  4. "Raggy rope, don't be a dope!" Poison ivy vines on trees have a furry "raggy" appearance. This rhyme warns tree climbers to be wary. Old, mature vines on tree trunks can be quite large and long, with the recognizable leaves obscured among the higher foliage of the tree.
  5. "One, two, three? Don't touch me."
  6. "Berries white, run in fright" and "Berries white, danger in sight."
  7. "Red leaflets in the spring, it's a dangerous thing." This refers to the red appearance that new leaflets sometimes have in the spring. (Note that later, in the summer, the leaflets are green, making them more difficult to distinguish from other plants, while in autumn they can be reddish-orange.)
  8. "Side leaflets like mittens, will itch like the dickens." This refers to the appearance of some, but not all, poison ivy leaves, where each of the two side leaflets has a small notch that makes the leaflet look like a mitten with a "thumb." (Note that this rhyme should not be misinterpreted to mean that only the side leaflets will cause itching, since actually all parts of the plant can cause itching.)
  9. "If butterflies land there, don't put your hand there." This refers to the fact that some butterflies land on poison ivy, since they are not affected, which provides them protection as their predators avoid eating the plant.
  10. "If it's got hair, it won't be fair." This refers to the hair that can be on the stem and leaves of poison ivy.

Effects on the body

Urushiol-induced contact dermatitis
Urushiol-induced contact dermatitis
Urushiol-induced contact dermatitis is the medical name given to allergic rashes produced by the oil urushiol, which is contained in various plants, including the plants of the genus Toxicodendron , other plants in the family Anacardiaceae Urushiol-induced contact dermatitis (also called...

 is the allergic reaction
Allergy
An Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid...

 caused by poison ivy. In extreme cases, a reaction can progress to anaphylaxis
Anaphylaxis
Anaphylaxis is defined as "a serious allergic reaction that is rapid in onset and may cause death". It typically results in a number of symptoms including throat swelling, an itchy rash, and low blood pressure...

. Around 15% to 30% of people have no allergic reaction. Most people will become sensitized with repeated or more concentrated exposure to urushiol, as the immune system has been trained to act with greater degree.

Over 350,000 people are affected by poison ivy annually in the US.

The pentadecylcatechols of the oleoresin within the sap of poison-ivy and related plants causes the allergic reaction; the plants produce a mixture of pentadecylcatechols, which collectively is called urushiol. After injury, the sap leaks to the surface of the plant where the urushiol becomes a blackish lacquer
Lacquer
In a general sense, lacquer is a somewhat imprecise term for a clear or coloured varnish that dries by solvent evaporation and often a curing process as well that produces a hard, durable finish, in any sheen level from ultra matte to high gloss and that can be further polished as required...

 after contact with oxygen.

Urushiol binds to the skin on contact, where it causes severe itching that develops into reddish coloured inflammation or non-coloured bumps, and then blister
Blister
A blister is a small pocket of fluid within the upper layers of the skin, typically caused by forceful rubbing , burning, freezing, chemical exposure or infection. Most blisters are filled with a clear fluid called serum or plasma...

ing. These lesions may be treated with Calamine
Calamine
Calamine is a mixture of zinc oxide with about 0.5% ferric oxide . It is the main ingredient in calamine lotion and is used as an antipruritic to treat mild pruritic conditions such as sunburn, eczema, rashes, poison ivy, chickenpox, and insect bites and stings...

 lotion, Burow's solution
Burow's solution
Burow's solution is a pharmacological preparation made of aluminium acetate dissolved in water. It was invented in the mid-19th century by Karl August Burow, an ophthalmologist....

 compresses or baths to relieve discomfort, though recent studies have shown some traditional medicines to be ineffective. Over-the-counter products to ease itching—or simply oatmeal baths and baking soda—are now recommended by dermatologists for the treatment of poison ivy.

The oozing fluids released by scratching blisters do not spread the poison. The fluid in the blisters is produced by the body and it is not urushiol itself. The appearance of a spreading rash indicates that some areas received more of the poison and reacted sooner than other areas or that contamination is still occurring from contact with objects to which the original poison was spread. The blisters and oozing result from blood vessels that develop gaps and leak fluid through the skin; if the skin is cooled, the vessels constrict and leak less. If poison ivy is burned and the smoke then inhaled, this rash will appear on the lining of the lungs, causing extreme pain and possibly fatal respiratory difficulty. If poison ivy is eaten, the mucus lining of the mouth and digestive tract can be damaged. A poison ivy rash usually develops within a week of exposure and can last anywhere from one to four weeks, depending on severity and treatment. In rare cases, poison ivy reactions may require hospitalization.

Urushiol oil can remain active for several years, so handling dead leaves or vines can cause a reaction. In addition, oil transferred from the plant to other objects (such as pet fur) can cause the rash if it comes into contact with the skin. Clothing, tools, and other objects that have been exposed to the oil should be washed to prevent further transmission.

People who are sensitive to poison ivy can also experience a similar rash from mangoes. Mangoes are in the same family (Anacardiaceae
Anacardiaceae
Anacardiaceae are a family of flowering plants bearing fruits that are drupes and in some cases producing urushiol, an irritant. Anacardiaceae include numerous genera with several of economic importance. Notable plants in this family include cashew , mango, poison ivy, sumac, smoke tree, and marula...

) as poison ivy; the sap of the mango tree and skin of mangoes has a chemical compound similar to urushiol. A related allergenic compound is present in the raw shells of cashew
Cashew
The cashew is a tree in the family Anacardiaceae. Its English name derives from the Portuguese name for the fruit of the cashew tree, caju, which in turn derives from the indigenous Tupi name, acajú. It is now widely grown in tropical climates for its cashew nuts and cashew apples.-Etymology:The...

s. Similar reactions have been reported occasionally from contact with the related Fragrant Sumac (Rhus aromatica
Rhus aromatica
Rhus aromatica is a plant species in the family Anacardiaceae native to Canada and the United States....

) and Japanese lacquer tree. These other plants are also in the Anacardiaceae family.

Similar-looking plants

  • Virgin's Bower (Clematis virginiana
    Clematis virginiana
    Clematis virginiana Clematis virginiana Clematis virginiana (also known as Devil's Darning Needles, Devil's Hair, Love Vine, Traveller's Joy, Virgin's Bower, Virginia Virgin's Bower, Wild Hops , and Woodbine; syn. Clematis virginiana L. var...

    ) (also known as Devil's Darning Needles, Devil's Hair, Love Vine, Traveller's Joy, Virginia Virgin's Bower, Wild Hops, and Woodbine; syn. Clematis virginiana L. var. missouriensis (Rydb.) Palmer & Steyermark [1]) is a vine of the Ranunculaceae family native to the United States. This plant is a vine that can climb up to 10–20 ft tall. It grows on the edges of the woods, moist slopes, and fence rows, and in thickets and streambanks. It produces white, fragrant flowers about an inch in diameter between July and September.

  • Box-elder (Acer negundo
    Acer negundo
    Acer negundo is a species of maple native to North America. Box Elder, Boxelder Maple, and Maple Ash are its most common names in the United States...

    ) saplings have leaves that can look very similar to those of poison ivy, although the symmetry
    Symmetry
    Symmetry generally conveys two primary meanings. The first is an imprecise sense of harmonious or aesthetically pleasing proportionality and balance; such that it reflects beauty or perfection...

     of the plant itself is very different. While box-elders often have five or seven leaflets, three leaflets are also common, especially on smaller saplings. The two can be differentiated by observing the placement of the leaves where the leaf stalk meets the main branch (where the three leaflets are attached). Poison ivy has alternate leaves, which means the three-leaflet leaves alternate along the main branch. The maple (which the box-elder is a type of) has opposite leaves; another leaf stalk directly on the opposite side is characteristic of box-elder.

  • Virginia creeper
    Parthenocissus quinquefolia
    Virginia creeper, five-leaved ivy, or five-finger is a woody vine native to eastern and central North America, in southeastern Canada, the eastern and central United States, eastern Mexico, and Guatemala, west as far as Manitoba, South Dakota, Utah and Texas.-Growth:It is a prolific climber,...

     (Parthenocissus quinquefolia) vines can look like poison ivy. The younger leaves can consist of three leaflets but have a few more serrations along the leaf edge, and the leaf surface is somewhat wrinkled. However, most Virginia creeper leaves have five leaflets. Virginia creeper and poison ivy very often grow together, even on the same tree. Be aware that even those who do not get an allergic reaction to poison ivy may be allergic to the oxalate crystals in Virginia creeper sap.

  • Western Poison-oak (Toxicodendron diversilobum‎) leaflets also come in threes on the end of a stem, but each leaflet is shaped somewhat like an oak
    Oak
    An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...

     leaf. Western Poison-oak grows only in the western United States and Canada, although many people will refer to poison ivy as poison-oak. This is because poison ivy will grow in either the ivy-like form or the brushy oak-like form depending on the moisture and brightness of its environment. The ivy form likes shady areas with only a little sun, tends to climb the trunks of trees, and can spread rapidly along the ground.

  • Poison Sumac (Toxicodendron vernix) has compound leaves with 7–15 leaflets. Poison sumac never has only three leaflets.

  • Kudzu
    Kudzu
    Kudzu is a plant in the genus Pueraria in the pea family Fabaceae, subfamily Faboideae. It is a climbing, coiling, and trailing vine native to southern Japan and southeast China. Its name comes from the Japanese name for the plant, . It is a weed that climbs over trees or shrubs and grows so...

     (Pueraria lobata) is a non-toxic edible vine that scrambles extensively over lower vegetation or grows high into trees. Kudzu is an invasive species
    Invasive species
    "Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....

     in the southern United States. Like poison ivy, it has three leaflets, but the leaflets are bigger than those of poison ivy and are pubescent underneath with hairy margins.

  • Blackberries and raspberries
    Raspberry
    The raspberry or hindberry is the edible fruit of a multitude of plant species in the genus Rubus, most of which are in the subgenus Idaeobatus; the name also applies to these plants themselves...

     (Rubus spp.) can resemble poison ivy, with which they may share territory; however, blackberries and raspberries almost always have thorns on their stems, whereas poison ivy stems are smooth. Also, the three-leaflet pattern of some blackberry and raspberry leaves changes as the plant grows: Leaves produced later in the season have five leaflets rather than three. Blackberries and raspberries have many fine teeth along the leaf edge, the top surface of their leaves is very wrinkled where the veins are, and the bottom of the leaves is light minty-greenish white. Poison ivy is all green. The stem of poison ivy is brown and cylindrical, while blackberry and raspberry stems can be green, can be squared in cross-section, and can have prickles. Raspberries and blackberries are never truly vines; that is, they do not attach to trees to support their stems.

  • The thick vines of Riverbank Grape
    Vitis riparia
    Vitis riparia Michx, also commonly known as River Bank Grape or Frost Grape, is a native American climbing or trailing vine, widely distributed from Quebec to Texas, and Montana to New England. It is long-lived and capable of reaching into the upper canopy of the tallest trees...

     (Vitis riparia), with no rootlets visible, differ from the vines of poison ivy, which have so many rootlets that the stem going up a tree looks furry. Riverbank grape vines are purplish in colour, tend to hang away from their support trees, and have shreddy bark; poison ivy vines are brown, attached to their support trees, and do not have shreddy bark.

  • Fragrant Sumac
    Rhus aromatica
    Rhus aromatica is a plant species in the family Anacardiaceae native to Canada and the United States....

     (Rhus aromatica) has a very similar appearance to poison ivy. While both species have three leaflets, the center leaflet of poison ivy is on a long stalk, while the center leaflet of fragrant sumac does not have an obvious stalk. When crushed, fragrant sumac leaves have a fragrance similar to citrus while poison ivy has little or no distinct fragrance. Fragrant sumac produces flowers before the leaves in the spring, while poison ivy produces flowers after the leaves emerge. Flowers and fruits of fragrant sumac are at the end of the stem, but occur along the middle of the stem of poison ivy. Fragrant sumac fruit ripens to a deep reddish color and is covered with tiny hairs while poison ivy fruit is smooth and ripens to a whitish color.

  • Hoptree (Ptelea trifoliata) has leaves that are remarkably similar. It is, however, a much larger plant so confusion is unlikely for any but the smallest specimens. The flowers and seeds are also easily distinguished from those of poison ivy.

  • Apios
    Apios
    Apios is a genus of flowering plants in the legume family, Fabaceae. It belongs to the sub family Faboideae....


External links

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