Poison Ivy

17 Feb

Toxicodendron radicans

(The misnomer “Poison-Oak” is applied sometimes to this species, although in Florida that name is probably best reserved for the close relative Toxicodendron pubescens and relatives in the Western U.S.)

Anacardiaceae, the Cashew Family, many of which can cause dermatitis


Continuing our month-of-Fridays probe into the botany of the Kiplinger Nature Preserve today in perfect weather, John and I found the plant most interestingly in bloom to be poison ivy.    Too bad it is nasty, because the species has a certain charm and fascinating natural history otherwise.


Leaflets 3 let it be.   All photos by brave John Bradford.

Poison Ivy is not “a” species, but rather the most mind-boggling complex of Mother Nature’s messy handiwork you can find.   Anyone who wants to reduce botany to simplistic species and easy rules better first look at this perplexing tangle of variation ranging across much of Asia, North America, and parts of Tropical America, but neither Europe nor Africa.      Different people can look into the complex and see different species, subspecies, varieties, and even different genera,  with our well known eastern Poison Ivy more similar to the same species in Japan than it is to all the numerous variants in the rest of the U.S. and Mexico.   The big ol’ mess was sorted out painstakingly by Michigan State University botanist William Gillis on the shoulders of predecessors.  The late Dr. Gillis and I shared the distinction of our careers intersecting with the only botanist convicted of booking  a hitman to murder his wife.

A good segue into Poison Ivy.  The writing on P.I. as a poison are infinite, so to pick the weirdest aspect of that history  I know of, as documented by Gillis, hereyago:  indigenous men in California used the irritating plants to oppress women.  When the men wanted to meet and keep the women apart, one guy would strip naked, be body painted, and run around all crazy threatening the women with wet poison ivy branches suspended around his head.   Who would volunteer for that job?  The hazards are numerous.  A better use of the plant, despite the itch, was in the Netherlands to reinforce dikes. Worked better than a little boy sticking his finger in the leak.


Would you believe Poison Ivy has a role in ornamental horticulture?    It develops red fall color and contributes to the subtle autumn hues in South Florida.     It has served in that capacity cultivated in gardens in climates where fall color is otherwise deficient.

Poison Ivy has the ability to resurrect dead trees.   The vine climbs hugging the defunct trunk, and way up high decides to branch out like the original limbs on the tree.   From the distance such a tree looks like a very odd species. Here is the vine covering a dead tree in flames. CLICK

We’ve been trying to catch it in bloom, so today was a minor triumph.   The flowers are separately male or female, on distinct plants.    In some locales, the male plants have foliage differing from the females, a weird occurrence.  Why?


Blooming P.I. today 2/17/17

The flowers draw bees, and Poison Ivy honey is not unheard of.   No thank you. The blossoms mature into little “berries” which are not berries; they are related to and resemble mini-mangoes: lopsided, flattened, and with a “stone.”  As the fruits age, the outer layer separates from the stone leaving a hollow space, and the outer layer can crack open along lines.

To wrap up, one more oddity.  Commonly allergic reactions come from proteins.    Poison Ivy causes a horrid allergic reaction yet its toxin is not a protein.   Oh however can that be?  Apparently the plant’s poison, urushiol, binds and alters proteins in human skin, and then those altered self-protein complexes kick off an allergy, sort of a vine-mediated auto-immune disorder.    The itchy oil is almost a varnish.   It can collect in sufficient quantities on the leaves to dry into a black spotty paintjob, a skull and crossbones reminder.   Fact is, the Chinese Lacquer Tree is itself likewise a species of Toxicodendron.



Posted by on February 17, 2017 in Uncategorized


9 responses to “Poison Ivy

  1. Nancy West

    February 18, 2017 at 11:47 am

    Hi, just a FYI, the monarch photo on the website is actually a monarch mimic, the Viceroy. I thoroughly enjoy your Treasure Coast posts and look forward to it every week. Thanks! Nancy West


    • George Rogers

      February 18, 2017 at 12:26 pm

      Nancy, Thanks, always glad for butterfly help. Tried to check it out, but I do not know where on our treasurecoastnatives website the butterfly is…can’t think of one…Maybe on an older archived post? They go back years. Or maybe right before my eyes, if it were a snake it would bite me.

  2. theshrubqueen

    February 18, 2017 at 4:44 pm

    From Batman to indigenous Californians, people just can’t resist three leaves or leave it be. Go figure, though I swear it looks different further north in the woods.

    • George Rogers

      February 18, 2017 at 10:04 pm

      Poor Batman. Poison Ivy is not his friend. As you go around the U.S., even around Florida you encounter so many variants they have keep taxonomists scratching, some have lobed leaflets, some not, some are shrubs instead of vines, some have leaflets with fancy outlines, some differ in flowers and fruits. Everywhere you go they differ. Thee are places where to different “species” occur together. Technically, depending on which classification you like, there are multiple species, two here in Florida, more as you go beyond, Fun to see, but not to organize. You should see the “book” by the world’s PI authority (besides Batman) William Gillis, mind-boggling it all is.

      • theshrubqueen

        February 19, 2017 at 8:12 am

        Having spent a lot of time in the woods in North Georgia – the PI looks pretty much the same there, so not true here, i am amazed I haven’t gotten a rash!

  3. Chris Lockhart

    February 18, 2017 at 11:30 pm

    Poison ivy is an interesting vine. Thanks for covering it! One thing I find interesting is a study on how more potent it is as CO2 levels rise. Mohan 2006, in

    • George Rogers

      February 19, 2017 at 9:39 am

      Thanks Chris. Will find the reference. Before that…is the implication that it grows more robustly with a C02 boost, and then being more robust, more prone to do all it does, including making its irritating :oil”? Or something else? What I don’t really get is the adaptive value of the toxin…I suppose it is “rough on proteins,” whether they be in an insect pest’s eating system or my wrist. Wonder how much that sort of thing has been studied…the actual protection from the toxin, and its mode of action. May exist-never looked. Curious now. Will find and read the reference you sent.

      • Chris Lockhart

        February 19, 2017 at 1:33 pm

        I don’t recall that it discussed more robust growth in general, though I wouldn’t be surprised considering how lush the earth was during previous periods of high CO2. I believe it was more on testing the levels of urushiol. I’ll email you another paper. One was more readable than the other.

  4. Chris Lockhart

    February 19, 2017 at 10:29 pm

    It turns out it is both more robust growth and increased urushiol. Glad it will be of use to your class.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: