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Poison Ivy

Toxicodendron radicans

Summary 6

Toxicodendron radicans, commonly known as eastern poison ivy or poison ivy, is a poisonous Asian and North American flowering plant that is well known for causing an itching, irritating, allergic and sometimes painful rash in most people who touch it, caused by urushiol, a clear liquid compound in the plant's sap. The species is variable in its appearance and habit, and despite its common name it is not a true ivy (Hedera), but rather a member of the cashew and almond family. Toxicodendron radicans is commonly eaten by many animals, and the seeds are consumed by birds, but poison ivy is most often thought of as an unwelcome weed.

At the Garden 7

Poison ivy is widespread in natural areas of the Garden, including around Twin Lakes, the Thain Family Forest, and elsewhere.

Description 8

The deciduousleaves of T. radicans are trifoliate with three almond-shaped leaflets. Leaf color ranges from light green (usually the younger leaves) to dark green (mature leaves), turning bright red in fall; 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 3–12 cm (1.2–4.7 in) long, rarely up to 30 cm (12 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 rhizomes or root crowns. The milky sap of poison ivy darkens after exposure to the air.

The urushiol compound in poison ivy is not a defensive measure; rather, it helps the plant to retain water. It is frequently eaten by animals such as deer and bears.

Toxicodendron 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 8 cm (3.1 in) above the leaves. The berry-like fruit, a drupe, mature by August to November with a grayish-white colour. Fruits are a favorite winter food of some birds and other animals. Seeds are spread mainly by animals and remain viable after passing through the digestive tract.

Distribution and habitat 8

Toxicodendron radicans grows throughout much of North America, including the CanadianMaritime provinces, Quebec, Ontario, Manitoba, and all U.S. states east of the Rocky Mountains, as well as in the mountainous areas of Mexico up to around 1,500 m (4,900 ft). Caquistle or caxuistle is the Nahuatl term for the species. It is normally found in wooded areas, especially along edge areas where the tree line breaks and allows sunshine to filter through. It also grows in exposed rocky areas, open fields and disturbed areas.

It may grow as a forestunderstory 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 the Southeastern United States. The similar species T. diversilobum (western poison oak) and T. rydbergii (western poison ivy) are found in western North America.

Toxicodendron radicans rarely grows at altitudes above 1,500 m (4,900 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 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 be mistaken for tree limbs at first glance.

It grows in a wide variety of soil types, and soil pH from 6.0 (acidic) to 7.9 (moderately alkaline). It is not particularly sensitive to soil moisture, although it does not grow in desert or arid conditions. It can grow in areas subject to seasonal flooding or brackish water.

It is more common now than when Europeans first arrived in North America. The development of real estate adjacent to wild, undeveloped land has engendered "edge effects", enabling poison ivy to form vast, lush colonies in these areas. It is listed as a noxious weed in the US states of Minnesota and Michigan and in the Canadian province of Ontario.

Outside North America, T. radicans is also found in the temperate parts of Asia, in Japan, Taiwan, the Russian islands of Sakhalin and the Kuriles, and in parts of China.

A study by researchers at the University of Georgia found that poison ivy is particularly sensitive to carbon dioxide levels, greatly benefiting from higher concentrations in the atmosphere. Poison ivy's growth and potency has already doubled since the 1960s, and it could double again once carbon dioxide levels reach 560 ppm.

Sources and Credits

  1. (c) Greg Lasley, some rights reserved (CC BY-NC), uploaded by Greg Lasley
  2. (c) James Mickley, some rights reserved (CC BY-NC), uploaded by James Mickley
  3. anonymous, no known copyright restrictions (public domain), http://commons.wikimedia.org/wiki/File:Illustration_Rhus_toxicodendron0.jpg
  4. (c) H. Zell, some rights reserved (CC BY-SA), http://commons.wikimedia.org/wiki/File:Toxicodendron_radicans_002.JPG
  5. (c) R. A. Nonenmacher, some rights reserved (CC BY-SA), http://commons.wikimedia.org/wiki/File:Toxicodendron_radicans_01671.jpg
  6. (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Toxicodendron_radicans
  7. (c) bkmertz, some rights reserved (CC BY-SA)
  8. Adapted by bkmertz from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Toxicodendron_radicans

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