Poison Oak--Toxidodendron diversilobum
(Reprinted from Gene's 2005 Wordpress post on our old blog)
On our recent run up Mt. Lemmon, we encountered an unusually large amount of poison ivy. Fortunately, being fall, it was mostly yellow/red/orange and easily spotted and hopefully avoided. What follows is the poison ivy story.
Poison ivy is a common name for Toxicodendron (sometimes Rhus) radicans. Okay, let me back up a little. As even my baby sister knows, all plants have Latin names that are indicative of their relationships with other plants. The most commonly used parts of that entire Latin name are the genus (in this case Toxicodendron) and species (radicans). Toxicodendron is used by some botanists and Rhus is used by others. Neither is right or wrong, people just don’t agree for various reasons. I like Toxicodendron. It means ‘poison tree’! Radicans means coming up from the roots, which poison ivy likes to do. (Don’t let this fool you, though. All plant names are not as descriptive as this.) All of this is pertinent because in our country we have three Toxicodendrons. T. radicans is what we have in our mountains extending from the middle west to the east side of the west coastal mountains and it is called ‘poison ivy’. In the east of our country is ‘poison sumac’, Toxicodendron vernix and typically, Pacific coastal is T. diversilobum, ‘poison oak’. Common names are a real source of confusion, as people don’t always know where one species starts and the other stops. Also, the three species vary somewhat, across their range, especially our poison ivy.
Very generally, here are the descriptions:
Our poison ivy is a low creeper, usually not more than 18 inches tall and sometimes climbing adjacent trees. It grows in patches in canyon bottoms and along stream sides, normally not lower than about 3000 feet and no higher than 8000 feet. It has three leaflets comprising the leaf, and they are mostly pointed, with slightly jagged edges. During the warm growing season, the plants are bright green, turning red/orange/yellow in fall, just before winter dormancy, at which time, they lose all of their leaves.
Poison oak is similar in leaf arrangement (three leaflets) to poison ivy, but the leaflet points are more rounded, suggesting an ‘oak’ leaf. This species is more of a vining plant, reaching several feet into and onto adjacent plants.
Poison Sumac--Toxicodendron vernix
Poison sumac is a full blown shrub up to several feet tall. The leaflets are pointed like poison ivy, but more than three. There can be as many as nine or more per leaf, although always an odd number of leaflets because of the single terminal one.
In the course of our running here in southern Arizona, we run by 4 species of Rhus (plants in this genus are not allergenic). These are all shrubby plants 3 to 6 feet high and are typical, leathery leaved, chaparral type plants. These plants, and the Toxicodendrons, are in the same family as cashew (Anacardiaceae), whose fruit and uncooked nuts are poisonous, and they are closely related to the eastern asian tree that produces the sap used in Chinese and Japanese lacquer ware. This lacquer contains the urushiol oil that is the allergenic ingredient in all Toxicodendrons. Fortunately, once hardened, this lacquer is not a problem. The urushiol oil is produced by the plant and is on all parts of it, leaves, stems and roots. It only takes a minute amount of urushiol to affect people. (Animals are not affected, although they can carry the oil on their fur.) It is estimated that 80% of the population is allergic to urushiol and it doesn’t seem to matter which species of toxicodendron it comes from. Also, an individual’s sensitivity can change over time, both becoming allergic and also resistant and then changing again! It gets worse. Breathing the smoke of burning poison ivy (or the other T.’s) can be a terrible experience to those who are sensitive. Urushiol oil can remain on the dead or dormant plant or on your running shoes for several years and still be allergenic. Once you are in this mess, though, the good news is that a thorough washing with soap (Fels Naptha works well–find it in the laundry section) will dissolve the oil so that it is washed away. If you are infected, and this can happen very quickly (literally minutes), the washing will limit the rash. Poison ivy infection is not spread by scratching the blisters. You can only infect new areas by moving the urushiol oil to another location. Washing thoroughly will stop the spread. In the 20 plus years that I have been running in PI habitat, I have gotten only a couple of small patches of rash. Also, I have never washed my shoes! I do try to dance through the plants, avoiding as much direct contact as possible.
Treatment methods: Go here http://poisonivy.aesir.com/view/cures.html
If you are still reading this, I suppose that you are avoiding doing something else. So here is a little more.
I would be remiss if I didn’t tell you about this other Poison Ivy. She makes up about 50% of the images in a search. I don’t know her origins or her Latin name, but she always has red hair. I warn you to stay away!
You’re gonna need an ocean
Of Calamine lotion
You’ll be scratchin like a hound
The minute you start to mess around
Late at night while you’re sleepin’
Poison Ivy comes a creepin’ around!