Naturespeak A naturalist's view of the world

June 15, 2007

Pretty Poison

Filed under: Uncategorized — wykes @ 9:54 pm

   What do Dermatitis, Cashews, Japanese Lacquer Boxes and Indian Marking Nuts have in common? Well, for one, they are all related in topic to some “herbe a la puce” flowers I was examining yesterday along a wooded trail.  The flowering “puce” in question was a luxuriant Poison Ivy vine dangling threateningly low over the path. These infamous plants are allowed to bloom in relative obscurity because everyone avoids them like the plague. Few peer close enough to observe the gentler side of this irascible neighbor.

  Admittedly, the flower clusters are easy to overlook, but I’ve snapped a few shots for you to safely view (look here and here and here).  The clusters appear at the end of each growing vine tip – the axillary portion, according to botanists. Most of the visible petals are light yellow green with tufts of yellow at the center. There are hundreds of flowers on each cluster, and each individual flower has five petals spanning 5 mm across.  Male and female flowers are found on different plants, so the blooms in question would likely be the male flowers exhibiting their manliness in the form of pollen bearing anthers. I didn’t seek out a female plant, but I can lay your mind at ease and tell you that the female flower clusters are similar and that each individual flower produces one seed.

  Pollinators in the form of winged insects, such as so-called “sweat” bees (see here), actively seek this sweet nectar source. It is safe to say that they love this plant. In fact, animals especially like the foliage and dozen of bird species eat the nutritious white fall berries. Populations of over-wintering Yellow-rumped Warblers (or Butterbutts as they are affectionately known) depend on good Poison Ivy fruit crops.

  Humans appear to be the only local life form that cannot form a friendship with this plant.  The non-volatile oils that permeate the stem, leaves, flowers and berries cause us no end of trouble if we contact it. The thick oily sap is laced with an allergenic agent known as Urushoil (3-pentadecyl catechol).  There is no portion of the plant that is safe to touch, period. Even burning it presents the risk of inhaling the noxious fumes and irritating sensitive bronchial tubes.

  The name Urushoil comes from the Japanese word for the Lacquer Tree – Kiurushi. This tree has long been tapped for its thick black sap which hardens into the shiny varnish used to coat ornamental boxes.  The Kiurushi is in the same family as the Cashew, the oddly named Indian Marking Nut, and the Poison Ivy. All are members of the Anacardiaceae or Cashew Family, and all have urushoil in them. 

  Just to be complete, here is a segment from a medical site which discusses the properties of the nasty “u” oil: “Urushiol, a group of alkylcatechols, is found in the sap of poison-ivy plants. The allergic reaction has been traditionally thought to involve initial oxidation by which a protein-reactive quinone is formed. Recent work indicates that redox cycling in the skin, following penetration of the allergenic alkybenzenes, initially depletes local levels of endogenous-reducing equivalents such as NADH and glutathione. Further cycling results in the uncontrolled generation of radical species that exhibit protein reactivity. The urushiol is not volatile and can contaminate clothing, tools, and domestic animals. Under dry conditions, the chemical can remain harmful for long periods (Mulligan 1990,Schmidt et al. 1990). “

  Did you catch all of that?  If not, it basically says that the oil causes Dermatitis that is bubbly, raw, itchy and capable of spreading. I’ll spare you the graphic illustrations presented in the paper, since most of us are intimately familiar with the resulting rash. I can’t resist mentioning, though, the one photo that shows the case of an individual who accidentally wiped his derriere with Poison Ivy leaves – it is not a pretty thing.

  Because of urushoil, cashew nuts have to be heat treated before they can be safely eaten and I’m pretty sure the same is true of Indian Marking Nuts (although I’ve not a clue what they are).  Japanese lacquer workers have to be very careful as well. Some of these lacquer craftsmen have long claimed that they can become immune to the deleterious effects by chewing on the raw lacquer.  Natural food guru Euell Gibbons once claimed that we could achieve the same immunity to poison ivy by eating the young, less potent, leaves. 

  I need to state here and now that there is no such thing as immunity to Poison Ivy and that Euell Gibbons is dead.  It is true that some folks start off life with the ability to roll around naked in the stuff without effect while others catch it with a sideways glance.  The immunity wears down over with time and repeated exposures. That last nude roll in the ivy patch may well result in a clinical photo of your derriere on a medical site.

  The best defense in this case is learning how to identify it. Poison Ivy has three leaflets per leaf.  They are smooth, glossy, and edged with a few jagged “teeth.” It can grow as a ground-hugging vine or a woody tree climbing vine of massive proportions (see here – the tree is on the left and the Poison Ivy is on the right). The vines are normally hairy due to the abundance of aerial climbing roots. 

  I invite you to sneak a close look at some Poison Ivy flowers this week, if nothing more than to say that you did it (bragging rights). Should you contact the leaves, immediate washing usually takes care of the problem.  Euell Gibbons once said that a brisk rubbing with Jewelweed leaves will achieve the same desired effect, but for some reason I am hesitant to put that advice to the test.


  1. highly entertaining reading.
    here’s a little rhyme for you i learned in my camping endeavors: leaflets three, let it be. berries white, take flight!
    got my first case of poison ivy on my arm already this year, it took FOREVER to heal. these might be myths, but i heard your overall immune system plays a factor in whether or not your exposure to poison ivy results in how bad of a rash you get. i also heard that if you wash off the oils after touching poison ivy within a half hour, your chances of breaking out are very decreased. in working in my yard which is full of the stuff despite my efforts in eradicating this nuisance, i keep to this rule and haven’t gotten a rash for years until this year (must have missed a spot) and i know i come in frequent contact with the stuff.

    Comment by vanessa — June 17, 2007 @ 1:27 am

  2. Vanessa:
    I’m familiar with the “Leaflets Three, Let It Be,” but haven’t heard the “berries white” part. It’s a good general rule of thumb that white berries can be harmful (Doll’s Eye & Poison Sumac). I guess the only reason I hesitate to use the leaflet ditty much is that there are so many nice three leaved plants ot there. I hate to give them all a bad name. Strawberries, Trillium, and Jack-in-the-Pulpit are a few prime examples. I simply can’t let a lucious strawberry go uneaten. I’ll be sure to use the whole phrase next time – in which case we can’t go wrong (nor offend those people friendly three leaved plants out there).

    Comment by Gerry Wykes — June 17, 2007 @ 8:58 pm

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