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.