Summer is a very dry season here. Most annuals are dead. The herbaceous perennials are dormant. The woody plants look tired. There a very few flowers. About the time the eye has convinced the brain that no color will be seen today, the monotony is broken by a despised plant, the poison oak. Around here, poison oak can be drought deciduous. It loses its leaves in response to dry weather, but first they turn a stunning pinkish red. Plants that get water all summer will turn red in the fall in response to decreasing daylight like a typical deciduous plant. Usually the color change from place to place and plant to plant is spread out over a long period of time. However, in one particularly dry year, much of the poison oak turned red at the same time. It was like autumn in Vermont. Well, maybe not quite, but it was as close to autumn in Vermont as we are going to get around here.
Poison oak is ubiquitous in the local Santa Monica Mountains. I cannot think of a single park that lacks it. As one might expect, it is common in shady, dampish areas, like in the habitat type known as Southern Oak Woodlands. It is so common there that I joke that they should be called "Poison Oak Woodlands". However, it is a rugged plant and can also be found in rocky chaparral, the tangles of a riparian woodland, hot coastal sage scrub, and on low coastal bluffs just yards from the high tide line. One might admire the tenacity if the plant didn't have that one glaring fault.
Poison oak and poison ivy are usually dioecious. That is a fairly rare feature in the plant kingdom. It is said that the male flowers are more fragrant than the female ones. One time I was taking a picture of poison oak flowers and I smelled a nice, light, sweet fragrance. The best I could tell, it was coming from the poison oak and not a surrounding plant.
There are five toxicodendron species in the United States and every state except Alaska, Hawaii, and most of Nevada have a least one. I am using the name "poison oak" (western poison oak, Toxicodendron diversilobum) in this article because that is the species with which I am most familiar. However, the following information can apply to any of the species. For information on the different species, see Toni Leland's article "Gardening Hazards: Don't Touch That Poison Ivy!".
Humans are the only species that is affected by the poison oak rash. All other animals are immune. About 15% of the human population is immune. It is sometimes said that the Native Americans were immune, as some groups used the stems in basketry, but that fact that they had antidotes shows that not all were immune. It is not known if the immunity was genetic or acquired through accidental exposure as babies or indirect exposure before birth. It appears that modern Native Americans are not as immune as their ancestors were. This may be due to intermarriage with people of European or African ancestry, who generally are not immune, or it may be be due to not living the traditional outdoor lifestyle and getting early exposure.
Most poison oak lore has to do with antidotes. Some are pretty wild. Some seem to make some sense. Some sound risky. I am not a medical professional and do not advocate trying any of these. These are given for education and entertainment only.
- An acquaintance of mine was out hiking. He came upon a man eating young poison oak leaves. He said that that would give him immunity to the plant. My acquaintance did not know that man and never saw him again, so we do not know the results of his experiment. It might have worked. He might have spent the next five days in the hospital. We don't know. I don't think that one is worth trying.
- It is said that a person can be "vaccinated" against poison oak by drinking milk from a goat that has eaten poison oak or by eating honey made from the pollen of poison oak. However, urushiol (the irritating oil) does not get transferred to an animal's milk and poison oak pollen does not contain urushiol, so there is no scientific reason why this would work, if indeed it does work.
- Many odd substances have been used as preventatives or cures. These include ferric chloride, bleach, nightshade berries mixed with cream, gunpowder, molasses mixed with sulfur, horse urine, carbolic acid, kerosene, and sugar of lead.
- Many people swear by jewelweed as an antidote, but controlled experiments have shown it to be no more effective than the placebo. I will not disparage it, though. If something causes your mind to heal you, it is a cure, it is not? Jewelweed does not grow around here. The folk remedy in the West is mugwort.
What good is poison oak? It produces oxygen and helps prevent soil erosion, but so do all the other plants. What critical place does it have in the web of life? I half-jokingly say that it keeps people out and lets the forest animals and plants live in peace, but at this point, no one knows what essential role in nature the plant may play. Native Americans used poison ivy as a cure for warts. Warts are caused by viruses. So is the common cold. Maybe some research needs to done in that direction. Poison ivy might turn out to be useful in better understanding the immune system, which could lead to a cure for cancer.
My husband says that I am a fan of poison oak. I would not go that far. I would not even say that I like it. If it all went away, I would not mind. However, since we are stuck with it, we might as well make the best of it. I do not expect anyone to like poison oak as a result of this article. I do hope that you can come to appreciate on some level some of the features of poison oak and ivy.
This link shows a short video of an oak woodland and features poison oak turning red.
(Editor's Note: This article was originally published on April 18, 2011. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)