Toxicodendron radicans (L.) Kuntze

Remark The words or terms in red (actually dark orange) in the text are defined in a glossary.

may_26_10.gthmb can't be loaded. Toxicodendron radicans is a woody low shrub that is erect or trailing, or is a climbing vine. It is well known for its ability to produce urushiol, a skin irritant that causes an itching rash for most people, technically known as urushiol-induced contact dermatitis. The plant is native to North America. It is listed as a noxious weed in the U.S. states of Minnesota and Michigan and the Canadian province of Ontario where it readily forms colonies.

Toxicodendron radicans is a highly variable taxon and there is considerable disagreement over whether Toxicodendron radicans is one species with variations and varieties or subspecies, or many separate species. Many botanists recognize 7 subspecies in the Toxicodendron radicans species, namely:

Other botanists consider some of theses subspecies, like the radicans subspecies as mere varieties in the species. Other still, in Québec notably, consider a species like
  • Toxicodendron rydbergii as a variety of Toxicodendron radicans i.e. with the name Toxicodendron radicans var. rydbergii. This seems to point to the fact that the Toxicodendron genus is still not well-known enough biologically and one will have to wait for a while before botanists agree on the specificity of the taxon.

    The species belongs to the Anacardiaceae family.


    In classical Greek one of the meaning of τοξιcοσ (toxicos) is poison with which the tip of an arrow is soaked. In Latin this became toxicum with the same meaning and the more general meaning of poison and laudanum (an opium extract once used for various medical purposes and as a recreational drug), and this is the root of the word toxic and of its derivatives. In classical Greek δενδρον means tree, and all species of the Toxicodendron genus are shrubs or small trees that are quite toxic.

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    In Latin, the verb radicare means to root, and radicans is its present participle, the epithet refers then to the fact that Toxicodendron radicans roots easily.

    Common names

    The vernacular name of Toxicodendron radicans is Poison Ivy. The French vernacular names are Herbe à la puce, Herbe à puce, Sumac grimpant, Toxicodendron grimpant.


    Toxicodendron radicans has also been known as:


    It is quite important to be able to identify readily Toxicodendron radicans whether in its climbing or non climbing form; its field marks are : The leaflets may have smooth, scalloped or irregularly toothed margins but typically the lateral two leaflets have irregularly toothed outer leaf margins and smooth, untoothed inner leaf margins. The middle leaflet is generally larger than the two laterals.

    In contrast, le Parthenocissus quinquefolia (the Virginia Creeper), a non-poisonous vine often mistaken for poison ivy, has five leaflets radiating from one point of attachment. draw_b.jpg can't be loaded.



    The stems are initially light reddish green but become woody, brown; they are smooth (though older stems of climbing plants develop a very hairy appearance). They may trail along (or just under) the ground, sending frequent branches both out and up. They may grow upright, in a shrub form, which can reach 7 feet in height under good conditions. Or they may grow as a vine, up to 5 inches in diameter, climbing trees and fences by means of dense, dark, fibrous, aerial roots (giving the vines that hairy look). They are toxic.


    The caterpillars of Amorbia humerosana (Tortricid Moth sp.), Marathyssa basalis (Light Marathyssa), and Paectes oculatrix (Eyed Paectes) feed on the foliage despite its toxicity.


    Bees are attracted by the nectar and pollen. An individual plant may in fact have perfect flowers, staminate flowers only, pistillate flowers only, or both staminate and pistillate flowers.


    The fruits persist on the plant through winter and are a favorite winter food of some birds despite their toxicity..


    Toxicodendron radicans 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 also grows as a forest understory plant, although it is only somewhat shade tolerant. It is also common around lakes, swamps, and rivers. It is not particularly sensitive to soil moisture, and is not n indicator or uniquely associated with a particular community type, although it does not grow in desert or arid conditions. It grows in a wide variety of soil types, and soil pH from 6.0 (acidic) to 7.9 (moderately alkaline); It can grow in areas subject to seasonal flooding or brackish water.


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    Toxicodendron radicans grows throughout much of the eastern half of North America, including several states west of the Mississippi river, including several Canadian provinces. The plant is extremely common in suburban and exurban areas of New England, the Mid-Atlantic and Southeastern United States. The plant is also found in the Russian Far East: Kurile Islands and Sakhalin, in China, Japan and Taiwan. The plant has been introduced in Europe (as a revenge for some insult ?) The map shows the Canadian provinces and U.S.A. states where the plant can be found.


    Toxicodendron radicans is the most common of the urushiol producing plants in the North America. Contact with urushiol oil is the substance that causes an allergic rash in 85 to 90 % of the population. Even a tiny amount (1 nanogram, a billionth of a gram) of sticky, resin-like urushiol oil will case a skin reaction. 1/4 ounce of the potent oil would be enough to cause a rash on the entire population of the earth!

    Poison Ivy Facts:

    The only sure way to avoid poison ivy rash is avoiding contact with urushiol oil directly from the plant or indirectly from clothing, tools, or gear that comes into contact with the oil.

    Within fifteen minutes of exposure urushiol oil bonds with the skin and a rash is likely. A long rinsing wash with cold water is an effective way to remove the oil. Warm water opens the pores allowing more oil to bond with the skin and soap may spread the oil more effectively.

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    Animals generally are not susceptible to dermatitis induced by Toxicodendron radicans. It is an important winter food for Odocoileus virginianus (White-tailed deer). The foliage, branches, and fruit are eaten by the Ursus americanus (Black Bear), and Sylvilagus species (Cottontail rabbits). A wide variety of migrant and resident non game and upland game birds consume the fruits in fall and winter. Genera of the Picidae family (Woodpeckers and Flickers) are especially attracted to the fruit.

    In spite of its toxicity, Toxicodendron radicans was used by several American native tribes. The Houmas took a decoction of leaves as a tonic. The Algonquins of Québec are said to have rubbed the leaves on the skin affected by a reaction to Toxicodendron radicans (increasing the problem ?). The Cherokees used as decoction of the plant as an emetic. The Kiowas used the plant to heal running or non-healing sores; they rubbed the leaves over boils or skin eruptions (making them worse ?) The Navajos used the plant to poison arrows and chewed the leaves to insure good luck in gambling !


    The photos of the gallery were taken either with one of the following: Minolta DiMAGE 7, Canon PowerShot A530, Canon Xt Rebel, usually with the EF-S60mm f/2.8 Macro USM objective, Fujifilm A 610 and EPSON Perfection 1650 (scanner).

    The title in the window shows the date when the picture was taken, i.e. jan_30_06... would mean that the photo was taken on the 30th of January, the 06 is for the 6th picture taken that day. The month, day and picture number might be followed by a letter which I use to identify the system used to take the picture.

    Click on the thumbnails to get larger view. The original photos are usually in TIFF format, the photos shown are generally in JPEG format, often of dimensions one half (surface one quarter) for loading time reduction.


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    Twigs, buds

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    Leaves, leaflets

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    The leaf and folioles were scanned at 300 dpi, and the dimensions of the resulting picture divided by 2 (area divided by 4); this allows to measure the dimensions of the leaves.


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    Fruits, seeds

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