Trails in Northern California

Trails in Northern California

Leave No Trace!

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March 23, 2013

POISON OAK, Besides Preventing Rashes…

We hear about it a lot here in the Sacramento area, and my motive isn’t to address the well-known issues of allergic reaction, prevention, or treatment of it from contact with the oils carried in the stems. 

There are more interesting facts that are less widely circulated, and worth knowing. 

This "meadow" is carpeted by poison oak along One Eye Creek Trail near Georgetown, CA.
by Laura Sheffield

Poison oak is native to North America’s Pacific West Coast, south into Baja and north to British Columbia.  It lives in a variety of habitats up to elevations of 5,000-6,000 feet.  It is a woody shrub or vine, and looks rubbery with reddish hues, rather than having a usual bark like texture or color. 

Poison Oak is the most prevalent shrub in California! 
  Its habitats include the understories of mixed evergreen forests, woodlands, chaparral, coastal scrub sage, redwoods, and riparian areas. 


That "shrub" growing in front of the tree is poison oak in the Knickerbocker area, at Cool, CA.  Compare to the adult off to the right for size!
By Laura Sheffield
It has even earned the name diversilobum, the Latin term used to make reference to its diversity in form.  It thrives in undisturbed areas, but will invade pastures and recreation areas (trails).  This is one plant with flexible requirements!  It can grow in a variety of soil types, elevations, light intensities, temperatures, and water conditions.  It is NOT related to ivy.
Taken by Laura Sheffield

As an angiosperm in the Anacardiaceae family, it is deciduous, dioecious or polygamous. Poison oak has pinnately compound, alternate, trifoliate leaves. They can be rotund to ovate, with margins that are lobate, denticulate, serrulate, or entire, all of which may be present on a single plant.  One of its apparent survival skills is to masquerade as other surrounding plants. Leaves are in groups of 3, 5, 7, and some sources say 9.  At the tip of the stem is where you find a longer center leaf on a pediole and two leaves at the base of the pediole growing opposite of each other. Poison oak is spread by birds that eat the fruits, and it passage through their digestive tracts actually enables its germination by reducing its period of dormancy once it is deposited by the bird.  It is rhizomatous, and can be grown from cuttings of roots or stems (in other words, rototilling won’t get rid of it).  Poison oak blooms each spring with little bunches of small greenish white flowers where leaves attach to the stems. Being dioecious, the male plants have 5 stamen, 1 sterile pistil, 5 petals, and 5 sepals.  The female has a fertile pistil and reduced sterile stamens. The plant bears fruit that is also whitish green little round berries.
If you zoom in, the dark lines on the fruit contain the substance people are allergic to.
Taken by Laura Sheffield in Granite Bay, CA. in late fall.
Its blossoms are a good source of honey.  The plant is considered a good food source for black tailed deer and livestock, although ratings of palatability range from good to poor.  Nutritionally, it has been measured from cuttings throughout California to provide 24.2% crude protein in March to 6.5% in September, along with other important nutrients.

Aside from all that goodness, the endangered Bell’s vireo uses poison oak for its nesting sites! 
The ringtail, a fully protected mammal in California has a rare documented colony living in a Freemont cottonwood/Pacific poison oak woodland along the Sacramento River.
Of course the Native Americans found medicinal uses for poison oak said to include curing ringworm, removing warts, calluses, and corns.  It was used to cauterize sores and stop bleeding, and to treat rattlesnake bites.  The Chumash drank a decoction made with poison oak roots to treat dysentery. 

Most importantly, current research is

being done to develop a serum from the resin to desensitize people. 
Best of all, a bonus is the research that is using poison oak resin with AIDS patients to stimulate T-cell production!

The most intriguing article I found was a blog written by a guy who eats the new tiny leaves and does this several times a year, and has supposedly developed resistance to it!  Try it if you like, but don’t say I told you to!  Check out his blog at Eating Poison Oak
I have a friend who is trying it.  He ate leaves for several days while hiking this spring.  It took several days of this before he had some strange feeling in the roof of his mouth so he took a break.  No reactions of any kind and I will update you when he tries it again.  Not saying you should do it...


University of CA Agriculture & Natural Resources @

 edited 4-30-2013
Removed photos that were not showing up for readers on June 16, 2015