Hiking in the Redwood Forest

Poison-oak | Poison oak

Copyright 2005 - 2011 by Mario Vaden

"Leaves of three, let it be - berries white, a poisonous sight" - Poison oak is green in summer, but occassionally red.

Question: if poison oak has no leaves for about 6 months, how will you identifiy it for 6 months during the cool season? This page offers a few tips. More Photos can be viewed in the Poison-oak Photo Album. I have seen vines up to 180 feet tall with small trunks like poison-oak on steroids, and heard reports of 200 footers. The 180 footer had a stem about 3.5" diameter. In 2012, Zane Moore from California, sent me a photo of a huge specimen. He discovered one poison-oak trunk 27" circumference or 8.6" diameter. And that was thirty feet from another one with a 23" circumference trunk. Then there are others small enough to hide among a carpet of sorrel, barely over toe height.

3 leaflets poison-oak poison oak leaves

Poison-oak is a deciduous plant that grows throughout many parts of west coast in several climates ranging from sea level to about 5000 feet elevation. Because it's deciduous, the "leaves of 3" phrase is useless half the year. Its name can be spelled Poison-oak, but will be written here without the hyphen as well.

The diversity in leaf size and shape accounts for the Latin species name "diversilobum". The full name is Toxicodendron diversilobum or Rhus diversilobum. Common names are Pacific poison oak and Western poison-oak. Poison-oak flourishes in several local climates - where rainfall is 19 inches per year, or even among the ocean region Redwoods where rainfall exceeds 50 inches.

Poison oak can be identified by leaves, which are usually lobed. Sometimes there are no lobes, but lobes commonly exist. The leaves are compound leaves, each comprised of 3 leaflets, but occassionally having 5 or more leaflets.

Young leaves are often glossy red, turning glossy green, with 3 to 5 viens. Individual leaflets of each compound leaf vary from about 1/2" to 4" long. Individual leaflets may resemble an oak leaf. The tips of poison oak leaflets are typically rounded rather than pointed. The leaf surface is usually glossy. Flowers are green-white, about 1/4" in diameter, in clusters on a slim stalk. The fruits are white, resemble berries, and appear glossy and dry when ripe.

poison oak in the shadeThis is poison-oak in the shade: October. In another image, poison-oak has fuzzy bark on the twig. Therefore, smooth and fuzzy bark are not sufficient factors for identification. Ribes, or flowering current, is shown in one image with flaky bark on. That's one characteristic not common to poison-oak.

There is a striped stone inside the papery shell. The branching pattern is alternating, where twigs - as well as leaves and buds - emerge from the stem in an alternate fashion; one to the left, the next to the right, then left, then right. The twigs are not opposite branched like vine maple where pairs of twigs are directly opposite each other on the stem. In winter, the appearance of twigs prevents confusing this with maple.

As a shrub form, poison-oak can be as tall as a small vine maple. As a vine, poison oak can grow over 150 high, and may not have lower stems or leaves. Few vines with smooth bark grow on Pacific NW trees.

The primary problem with poison-oak is in its oily residue - urushiol; an oleoresin.

Approximately 10 percent of the United States population is estimated to be unaffected by urushiol - no rash. That leaves 90 percent of people who are susceptible to the reaction caused by poison oak and urushiol.

Everybody including the "immune" should be cautious, because "immunity" to poison oak may change. The term "immune" is a bit figurative, because it's the immune system that generates the minor and severe rashes from poison oak.

Urushiol is long lasting. It won't just go away in a short time like evaporating moisture. The substance can linger on gloves, clothing, tool handles, tarps, shoes and pet fur. Anything suspected to have contacted poison oak, should be discarded or washed. The urushiol can remain potent for months, even years. One resource records that centuries-old preserved specimens of poison oak caused dermatitis to people sensitive to urushiol. Urushiol can remain active on dead plants for as much as 5 years, and on unwashed clothing for a year or two.

Urushiol in poison oak is potent. It's estimated that the amount covering the head of a pin (50 micrograms) could make 500 people itch. That's less than a grain of salt which is 60 micrograms.

seed capsules winter Poison-oak IDPoison-oak "seed capsules". These appear summer to autumn. Color from ivory to white. A seed is within. Touching should be avoided. About 1/4 to 3/8 inches wide. Flowering current berries are dark.

The resin is also stable and long-lasting. Some people are so sensitive that a molecular trace of urushiol (2 micrograms: under 1 millionth of an ounce) can start an allergic reaction

Urushiol is in every part of poison oak: leaves, stems, roots, sap

Urushiol is a toxin or irritant found in: poison oak, poison ivy, poison sumac, lacquer plant of Asia, sometimes called the Chinese Lacquer or Chinese VarnishTree or

Depending on sensitivity and level of exposure, symptoms generally appear 12 to 48 hours later. Contrary to one popular belief, you can't get a poison oak rash from someone else Poison-oak is not contagious in other words. The liquid in your blisters is not urushiol, but fluids that your body produced. But, popping the blisters is not recommended because it can hinder healing, lead to infection or cause permanent scarring.

The oil from poison oak begins to permeate or bind with skin in as little as 5 to 10 minutes. The sooner you wash the exposed area - and a bit more skin area - the smaller your chances for significant rashes or blisters.

Wash with plenty of cool running water. Don't use soap that contains lanolin or other oils that could spread the urushiol more. Ivory soap and several other hand soaps will work fine.

poison oak twigThis is poison-oak: January. Compare the fuzzy, tan and segmented appearance of this tiny twig to the image of Ribes. Poison-oak can be confused in winter with flowering currant (Ribes sanguinium). Flowering currant often develops a similar form with upright angled twigs and branches. Both flowering currant and poison-oak can retain old stalks from flowers, or berries in winter. You can see that the buds are not the same. The Rhibes tends to have more prominent narrow pointed buds. Keep in mind that poison-oak stems are not always fuzzy. I have seen rather smooth young vines on trunks before, especially in the shade. But Rhibes does not cling to trunks as a vine.

Apply rubbing alcohol with cotton balls to the parts of the skin that are affected. That alchohol can help to alter the oil from poison oak. Still wash with plenty of soap and water. Warm water can open pores, so use cold water.

Taking a bath may result in urushiol reattaching if it floats and your body rises up through it again. Some people have claimed that showers can spread urushiol, but a shower is better than a bath. Most people that spread poison oak with a shower, probably did not wash their whole body thoroughly enough.

Wash the entire body with soap and water several times. If you ask the people who took inneffective showers about their shower, you will probably learn that they took a warm shower instead of a cold shower. Not many people will take a cold shower. If you want to shower off urushiol, you need to prepare to endure a cold shower for several washings over several minutes. Odds are that a lot of urushiol will get in skin before a shower can be reached. But leaving any residue can only make things worse.

The rash begins with itching and swelling, followed by a rosy inflammation of tiny pimples. Blisters can follow; exuding a clear oozing fluid which will crust-over. The rash, a histamine response, can last last 2 to 5 weeks. There is no cure for the poison oak rash once it begins, but we can relieve symptoms and discomfort. Minor itching, pain and swelling can be relieved with over-the-counter treatments which contain zinc acetate, hydrocortisone or zinc oxide. In severe cases, physician may prescribe antihistamine creams or medicine.

Burning poison oak is unwise. Fire may not destroy urushiol. Smoke can contain urushiol and carry it to clothing or into lungs if that smoke is inhaled. Poison oak should not be burned. It should be carefully cut, dug or pulled out. It can be cut into small pieces and buried. Do not include poison-oak in debris to be mulched for compost. Although nonvolatile, urushiol may be carried in ash and dust particles and as minute droplets in smoke from burning foliage.

Avoid pulling poison-oak vines off of tall woody plants like pines or firs. Falling residue can drop urushiol down onto unprotected skin. It may be better to sever the vines at the base of the tree and let the poison oak and urushiol deteriorate over time. For outdoor workers, hikers, firefighters and other people - poison oak, poison ivy or urushiol blocker is availablel.

ribes sanguinium pertaining to poisonoakCompare the form of this upright branching flowering currant (Ribes sanguinium) with the poison-oak plant. Ribes buds are not always this big and red in December as in this late January photo. But the buds tend to be more pointed than those of poison-oak. Note bark on small twigs is almost glossy.

Poison oak, poison ivy and poison sumac of the Rhus family grow in most regions of North American; ecluding Nevada, Alaska and Hawaii. Poison oak is uncommon above 4,000 feet elevation and areas with less than eight inches of rainfall per year.

Poison oak is a cause of workers compensation claims in the United States. In California, poison oak accounts for 1% of workers compensation claims. 1% is not a big number, but in California, 1% of anything is substantial. Poison oak and poison ivy are estimated to cause up to 10% of lost work time in the U. S. Forest Service during some years.

California's poison oak was noted by an 1800s British explorer, Captain Frederick Beechey, who brought samples back to England.

The first known written record of poison ivy in North America dates to the early 1600s from Captain John Smith. Both poison oak and poison ivy were planted in English gardens for the climbing habit and autumn color - but not without consequences to English gardeners.

In late spring loose clusters of small green-white flowers are produced in leaf axils: where the leaf meets or connects to the stalk. Male and female flowers are usually produced on separate plants; referred to as dioecious. Sometimes, unisexual and bisexual flowers may occur on the same poison oak plant; referred to as polygamous.

Male flowers have five stamens surrounded by five cream color petals; there is a pistil that is not fertile. Female flowers have fertile pistils in the center and stunted sterile stamens, surrounding.

Urushiol is found in resin canals within the plant and on plant surfaces if leaves and stems are bruised or damaged by insects. Uniquely, it does not occur in honey made from poison oak flowers. Regardless of urushiol's presence in resin canals within the plant, we know that brushing the leaves and stems transfers the oil from the exterior of the plant to our clothes and skin.

Poison oak oil penetrates the outer layer of the skin and binds to proteins of deeper skin cell membranes. Before the protein bond occurs, a more reactive substance - quinone - is oxidized; released. The reactive quinone bonds to white blood cell membranes deep in the skin.

After binding to membranes in skin, urushiol is virtually impossible to wash off. By itself the urushiol molecule wouldn't cause such a severe irritation, but once attached to cell membranes, it attracts defensive cells within the human body, triggering strong reactions.

Poison oak commonly has red fall color similar to the image at left. Some poison-oak plants look like this in summer, and new spring foliage can emerge red colored.

Sources include Native Plants: Portland Community College, California Poison Control System, Oregon State Univ. Extension Service, U.S. Dept. of Agriculture, Univ. of California, US Food and Drug Administration, Wikipedia.