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Anacardiaceae

Toxicodendron Mill.

Kingdom: Plantae Rank: Genus Parent: Anacardiaceae Status: Valid

Common Names:

  • POISON-OAK - English, United States of America
  • POISON-IVY - English, United States of America

Morphological Description

Diagnosis: Poisonous woody vines, shrubs, subshrubs, or small trees; leaves pinnately 3-foliate or pinnately compound, often turning bright red in fall.

Other

Ecology: All species are toxic in nature.

Notes: A genus of 15+ species of North and South America and e Asia; often included in the genus Rhus but rather clearly distinguished (Barkley 1937; Gillis 1971). These species are toxic, causing severe allergic contact dermatitis in some individuals. Physical contact with any part of the plant, exposure to fumes/smoke from burning plants, or contact with pets having touched the plants are common means of exposure. Following a latent period of 12-24+ hours after exposure, there is reddening of the skin, sometimes accompanied by edematous swelling. This can be followed by the formation of fluid-filled blisters; this fluid cannot spread the dermatitis. Instead, additional spread is from unwashed skin, clothing, or other objects (Lampe 1986). Eating the leaves can result in an internal reaction occasionally known to be fatal (Gillis 1975). According to Gillis (1975), "The poisons may be effective for an indefinite period of time in causing dermatitis. Several hundred year-old herbarium specimens have been known to affect a sensitive person who has handled them!" These reactions are caused by resinous phenolic compounds commonly known as urushiols (chemically pentadecylcatechols). Because the compounds are insoluble in water, washing with a strong soap as soon as possible after contact is recommended. Gillis (1975) and Frankel (1991) discussed Toxicodendron dermatitis. Gillis (1975) also gave several citations documenting the use of POISON-IVY in Native American arrow poisons. The sap of an Asian species, T. vernicifluum (Stokes) F.A. Barkley (ORIENTAL LACQUER TREE), is a major source of lacquer; furniture treated with the lacquer can cause dermatitis in sensitive individuals. Toxicodendron species, like those in the genus Rhus, often display very early fall foliage color (often strikingly red); this is considered to serve as a "foliar fruit flag" which attracts birds that act as dispersal agents for the fall-ripening fruits (Stiles 1984). (Latin: toxicum, poison, and Greek: dendron, tree)