Poison Oak

From REWILD.info Field Guide, the free Field Guide To Rewilding

Poison Oak
Toxicodendron diversilobum and pubescens
Western poison oak (larger leaves; small leaves are another plant) at base of oak tree
Scientific classification
Kingdom Plant Division Magnoliophyta Class Magnoliopsida Order Sapindales Family Anacardiaceae Genus Toxicodendron Species diversilobum and pubescens

[edit] Introduction

Western poison oak or Pacific poison oak (Toxicodendron diversilobum or formerly Rhus diversiloba) 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.

[edit] Western Poison Oak

[edit] Identification

Western poison oak is extremely variable in growth habit and leaf appearance (hence the specific name diversilobum/diversiloba meaning diverse lobes). 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. The leaves are divided into 3 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 generally bright green in the spring (or bronze when first unfolding), 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 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 sap may have oozed and dried.

[edit] Origin, Distribution, Habitat, and Life Cycle

Origin

Please help the REWILD.info Field Guide by providing this information.

Distribution

Western poison oak is found 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.

Habitat

Western poison oak is often found in oak woodlands and Douglas-fir (Pseudotsuga) forests. Along the Avenue of the Giants in northern California, the vine form may be seen climbing many feet up the trunks of Coast Redwoods (Sequoia sempervirens). It can also be found in damp, shady areas near running water and out of direct sunlight. Any trail leading to a waterfall on California's coast will most likely be home to western poison oak.

Life Cycle

Perennial

Phenology

Please help the REWILD.info Field Guide by providing this information.

[edit] Atlantic Poison Oak

Atlantic poison oak leaves

Atlantic poison oak (Toxicodendron pubescens or formerly Rhus pubescens) is an erect shrub that can grow to 1 m (3 ft) tall. The leaves are alternate, with three leaflets on each. The leaflets are usually hairy, and are variable in size and shape, but most often resembling white oak leaves. The leaves are usually 15 cm (6 in) long, turning yellow or orange in autumn. The fruits are small, round, and yellowish or greenish.

[edit] Origin, Distribution, Habitat, and Life Cycle

Origin & Distribution

This species is native to the Southeastern United States westward to Texas and Oklahoma.

Habitat

Atlantic poison oak can be found growing in forests, thickets, and dry, sandy fields.

Life Cycle

Perennial

Phenology

Please help the REWILD.info Field Guide by providing this information.

[edit] Toxin

Pacific Poison Oak

Poison oak leaves and twigs have a surface oil, urushiol, that is an allergenic irritant. Depending upon individual susceptibility (85% of humans will develop allergic reactions) and exposure, the symptoms can range from trivial to life threatening. The common effect is an irritating, itchy rash, often accompanied with blistering of the skin.

The oil can be transferred from one part of the body to another, from one person to another by contact or by transfer through an object (such as an automobile seat belt), from a pet to a person, or from clothing to skin when clothes are prepared for washing. If exposed, the recommended immediate treatment is to wash the exposed area with cold water, using sand or other mineral soil as an abrasive. Warm water will tend to open pores on the skin and will lead to deeper irritation. Tecnu brand waterless soap (available at many pharmacies and sporting goods stores in the western United States) has oderless mineral spirits as the active ingredient and will cut the oils before they can spread.

After the oil is removed, the poison oak cannot usually be spread by contact with an affected area or by scratching. However, scratching can open the skin especially in cases with significant blistering, making it possible for the skin to become infected by opportunistic bacteria (known as a secondary infection).

[edit] Treatment

Mild cases of poison oak rash are treated with calamine lotion, hydrocortisone cream, Aloe vera, and other drug store aids. Severe cases may require medical treatment and even hospitalization. Topical diphenhydramine (Benadryl) may provide relief in localized areas, but it should not be used on large areas of the body due to the potential for serious or life-threatening systemic side effects. Inhalation of smoke from burning poison oak can result in life-threatening lung damage.

For more information on poison oak rashes, see urushiol.

[edit] Gallery

Western Poison Oak
Green phase	Red phase	Climbing variation
Berries	Ground variation

[edit] See also

• Urushiol
• Poison Ivy
• Poison Sumac

[edit] External links

• American Academy of Dermatology - Poison Oak info
• Toxicodendron Dermatitis: Identification, Immunologic Mechanisms, Diagnosis, and Treatment
• NCRS: USDA Plants Profile: Toxicodendron pubescens

[edit] Disclaimer

[edit] Sources

Attribution

• Text copied from the following GNU Free Documentation License sources
  • Wikipedia:Western poison oak
  • Wikipedia:Atlantic poison oak

References