Difference between revisions of "Toxicodendron diversilobum"

Latest revision as of 11:27, 7 July 2010

Toxicodendron diversilobum (syn. Rhus diversiloba; Western Poison-oak or Pacific Poison-oak) is a plant best known for its ability to cause allergic rashes after contact. Western Poison-oak is found only on the Pacific Coast of the United States and of Canada. It is extremely common in that region, where it is the predominant species of the genus; the closely related Atlantic Poison-oak (T. pubescens) occurs on the Atlantic Coast. The hyphenated form "Poison-oak" is used, rather than "Poison Oak" to clearly indicate that it is not a variety of oak, just as "Poison-ivy" is not a variety of ivy.

Habitat

Western Poison-oak occurs only on the Pacific Coast, where it is common, and ranges from southern Canada to the Baja California peninsula. It is one of California's most prevalent woody shrubs but also climbs, vine-like, up the sides of trees, and can be found growing as single stems in grassland--often as part of early stage succession where woodland has been removed, and serving as a nurse plant for other species.

The plant often occurs in California oak woodlands and Douglas-fir (Pseudotsuga) forests. The vine form climbs far up the trunks of Coast Redwoods, potentially killing smaller trees.

It is found in damp, shady areas near running water and out of direct sunlight. Any trail leading to a waterfall on California's coast may likely be home to western poison-oak. Western poison-oak can also be found in some inland mountain ranges such as the Cascades.

Toxin

Western Poison-oak leaves and twigs have a surface oil, urushiol, which causes an allergic reaction. Around 15%^[1] to 30%^[2] of people have no allergic response, but most if not all will become sensitized over time with repeated or more concentrated exposure to urushiol.

Effects

Effects of Poison Oak are similar to those of Poison Ivy. It first causes severe itching, evolves into inflammation, non-colored bumps, and then blistering when scratched.

Appearance

Western Poison-oak is extremely variable in growth habit and leaf appearance. It grows as a dense shrub in open sunlight, or as a climbing vine in shaded areas. Like Poison ivy, it reproduces by creeping rootstocks or by seeds.^[3] The leaves are divided into three leaflets, 3.5 to 10 centimeters long, with scalloped, toothed, or lobed edges- generally resembling the leaves of a true oak, though the Western Poison-oak leaves will tend to be more glossy. Leaves are typically bronze when first unfolding, bright green in the spring, yellow-green to reddish in the summer, and bright red or pink in the fall. White flowers form in the spring and, if fertilized, develop into greenish- white or tan berries. Toxicodendron diversilobum is winter deciduous, so that after cold weather sets in the stems are leafless and bear only the occasional cluster of berries. Without leaves, poison oak stems may sometimes be identified by occasional black marks where its milky sap may have oozed and dried.

Botanist John Howell observed that Toxicodendron diversilobum's toxicity obscures its merits. "In spring the ivory flowers bloom on the sunny hill or in sheltered glade, in summer its fine green leaves contrast refreshingly with dried and tawny grassland, in autumn its colors flame more brilliantly than in any other native, but one great fault, its poisonous juice, nullifies its every other virtue and renders this beautiful shrub the most disparaged of all within our region." ^[4]

• PoisonOakGreenPhase.jpg

  Green phase

• PoisonOakRedPhase.jpg

  Red phase

• Toxicodendron diversilobum berries.jpg

  Berries

• Pacific-Poison-Oak.jpg

  Pacific Poison-oak

• PoisonOak wb smallerLeaves.jpg

  Ground variation

• ClimbingPoisonOak.jpg

  Climbing variation

See also

• Burow's solution, for treating the toxin
• Poison sumac

References

External links

• American Academy of Dermatology - Poison Oak info
• Western Poison-Oak Photo Gallery
• Poison Oak/Poison Ivy Information Centersv:Giftsumak

1. ↑ Howstuffworks "How Poison Ivy Works"
2. ↑ Contact-Poisonous Plants of the World
3. ↑ C.Michael Hogan (2008) "Western poison-oak: Toxicodendron diversilobum", GlobalTwitcher, ed. Nicklas Strömberg
4. ↑ Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.