Toxicodendron radicans

Toxicodendron radicans, commonly known as eastern poison ivy or poison ivy, is a species of allergenic flowering plant. It has numerous subtaxons and forms both vines and shrubs. Despite its common name, it is not a true ivy, but rather a member of the cashew and sumac family, Anacardiaceae. It is different from western poison ivy, Toxicodendron rydbergii, and resembles a number of species.

The species is found in North America. Although commonly eaten by animals, with birds consuming the seeds, T. radicans is considered a noxious weed. As a poison ivy, it causes urushiol-induced contact dermatitis in most people who touch it, producing an itchy, irritating, and sometimes painful rash.

Description

Numerous subspecies and/or varieties of T. radicans are known. They can be found growing in any of the following forms, all having woody stems:

as a climbing vine that grows on trees or some other support
as a shrub up to tall
as a trailing vine that is long.

The deciduous leaves of T. radicans are trifoliate with three almond-shaped leaflets. The leaf color ranges from light green (usually when young) to dark green (in maturity), turning red, orange or yellow in fall; some sources say the leaves are also reddish when expanding (before becoming dark green). The leaflets are long, rarely up to , and somewhat shiny in maturity. 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 rhizomes or root crowns. The milky sap of poison ivy darkens after exposure to the air.

T. radicans spreads either vegetatively or sexually. It is dioecious; flowering occurs from May to July. The yellowish- or greenish-white flowers are typically inconspicuous and are located in clusters up to above the leaves. The berry-like fruit, a drupe, mature by August to November with a grayish-white colour. The appearance of poison ivy can vary greatly among environments, and even within a large 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 rhymes describe the characteristic appearance of poison ivy:

"Leaves of three, let it be" is the best known and most useful cautionary rhyme. It applies to poison oak, as well as to poison ivy. However, some other innocuous plants have similar leaves.
"Hairy vine, no friend of mine"
"Berries white, run in fright" and "Berries white, danger in sight"

Taxonomy

;Subspecies

T. r. subsp. barkleyi Gillis
T. r. subsp. divaricatum (Greene) Gillis
T. r. subsp. eximium (Greene) Gillis
T. r. subsp. hispidum (Greene) Gillis
T. r. subsp. negundo (Greene) Gillis
T. r. subsp. pubens (Engelm. ex S. Watson) Gillis
T. r. subsp. radicans
T. r. subsp. verrucosum (Scheele) Gillis

Caquistle or caxuistle is the Nahuatl term for the species.

Distribution and habitat

T. radicans grows throughout much of North America, including the Canadian Maritime provinces, Quebec, Ontario, and all US states east of the Rocky Mountains, as well as in the mountainous areas of Mexico Poison ivy's growth and potency has already doubled since the 1960s, and it could double again once carbon dioxide levels reach 560 ppm.

Ecology

The fruits are a favorite winter food of some birds and other animals, including wild turkeys. Seeds are spread mainly by animals and remain viable after passing through the digestive tract. Birds may spread the seeds by regurgitation.

Toxicity

thumb|upright=1.3|A video describing the effects of poison ivy on the body

thumb|upright=1.3|[[Blisters from contact with poison ivy]]

Urushiol-induced contact dermatitis is the allergic reaction caused by poison ivy. In extreme cases, a reaction can progress to anaphylaxis. Around 15 to 25 percent of people have no allergic reaction to urushiol, but most people have a greater reaction with repeated or more concentrated exposure. Typically, the rash from the urushiol oil lasts about five to twelve days, but in extreme cases, it can last a month or more.

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

The pentadecyl catechols 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 after contact with oxygen.

Urushiol binds to the skin on contact, where it causes severe itching that develops into reddish inflammation or uncoloured bumps, and then blistering. These lesions may be treated with Calamine lotion, Burow's solution compresses, dedicated commercial poison ivy itch creams, 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 recommended by dermatologists for the treatment of poison ivy.

A plant-based remedy cited to counter urushiol-induced contact dermatitis is jewelweed, though jewelweed extracts had no positive effect in clinical studies. Others argue that prevention of lesions is easy if one practices effective washing, using plain soap, scrubbing with a washcloth, and rinsing three times within 2–8 hours of exposure.

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. If plant material with urushiol 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. An urushiol rash usually develops within a week of exposure and can last 1–4 weeks, depending on severity and treatment. In rare cases, urushiol 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.

Treatment

Immediate washing with soap and cold water or rubbing alcohol may help prevent a reaction. During a reaction, Calamine lotion or diphenhydramine may help mitigate symptoms. Corticosteroids, either applied to the skin or taken by mouth, may be appropriate in extreme cases. An astringent containing aluminum acetate (such as Burow's solution) may also provide relief and soothe the uncomfortable symptoms of the rash.

References

External links

Anacardiaceae in BoDD – Botanical Dermatology Database
Toxicodendron radicans images at bioimages. vanderbilt.edu
Poison Ivy, Ontario Ministry of Agriculture, Food and Rural Affairs
Common weeds of the northern United States and Canada: Western poison oak, poison ivy and poison sumac. (Anacardiaceae-family)
Large site with many photos, facts, products, rash images, and a quiz about poison ivy.