The official website of the Elkhorn Slough Foundation and Elkhorn Slough National Estuarine Research Reserve
Elkhorn Slough Plants: Poison Oak

Scientific Name:
Toxicodendron diversilobum

Family:
Anacardiaceae

Found at the Slough:
Upland woodland and riparian habitats.

Did you know...
Some animals eat poison oak's leaves and berries.

Poison oak is a vine or shrub that is native to California. In spring the foliage is bright green, in late summer it begins to turn red & slightly brownish-orange. Extremely variable, 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 three leaflets, 35-100 mm long, with scalloped, toothed, or lobed edges. Remember the rhyme, “leaves of three, let it be.” 

Poison oak contains a potent allergen known as urushiol. Urushiol, a skin irritating oil, produces variable reactions in 50 to 85 percent of the population, ranging from minor irritation to severe inflammation and blistering. In winter, poison oak loses its leaves but the stems remain and can still cause severe irritation, so hiking with legs covered and staying on trails can help prevent exposure.

Poison Oak in bloom.

If you have been exposed to poison oak while hiking, be mindful not to touch other areas of your body such as eyes and face or others as it can spread easily. When you return to your car, remove your exposed clothing and wash well with an oil cutting soap such as Technu. If a rash develops, it can be soothed with over the counter calamine lotions, but severe cases will require a more agressive treatment that only a doctor can prescribe.

Poison oak is widely distributed in the watershed, particularly moist, wooded areas and along freshwater waterways. It can be found throughout the Reserve, on all the trails. Ubiquitous in this part of California, people should be cognizant of its appearance.

Deer, birds, and other wildlife commonly eat the leaves and berries.  Interestingly, poison oak has high concentrations of phosphorous, sulfur, and calcium.  According to Gray & Greaves (1984), the federally endangered least Bell's vireo uses poison-oak for nest sites in oak woodlands.  Scientists have shown that cottonwood and poison oak woodlands contribute to overall bird diversity and density in California (Hehnke and Stone 1979).

 

 

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