Ah, the itchiness of the warm season........

As I sit here blogging, the back of my legs below the knees, my left forearm and half a dozen spots in between are plagued by a fiery, oozy  itch.  Don't worry, its just poison ivy.

I knew I was in for some fun a couple of weekends ago when I made the ridiculous choice to wear shorts into the Ozark woods (first time wearing shorts into the woods in years).  To be fair, we were simply visiting  various creek, pond and spring sites in search of dragonflies, how was I to know we would have to conquer barricades of poison ivy in order to do so?  Yes, I know what poison ivy looks like and I saw it everywhere we went even as it lightly caressed my calves.  I was completely unsurprised by the eruption of irritation upon my body several days later.

So, lets talk about poison ivy; the plant and the irritation.

We'll start with a gross picture.

Contact dermatitis caused by Poison Ivy

Poison Ivy, the irritation, is contact dermatitis caused by the plant of the same common name.  More specifically, it is the contact dermatitis caused by urushiol, an oil contained in all parts of the plant, especially in the sap.

Just for the record, poison ivy isn't the only plant known to cause contact dermatitis.  A number of texts refer to dermatitis caused by handling the flowers or leaves of Trumpet Creeper, aka Cow-itch Vine (Campsis radicans).

Trumpet Creeper foliage - despite trying, I have not been able to get contact dermatitis from this plant

Also, the interesting spring wildflower Dutchman's Breeches (Dicentra cucullaria) has been known to cause contact dermatitis in some people.

Beware the Dutchman's Breeches?

It is possible to wash the urushiol from your skin after contact, but this must be done very quickly.  One source I found said that 50% of the urushiol is absorbed into your skin in the first 10 minutes after contact.
If you hike frequently and routinely find yourself exposed to poison ivy, I highly recommend Tecnu.  This stuff works!  Simply applying it to my skin prior to and after known contact with poison ivy saved me a lot of itching.  It does smell kinda strange though.

Poison Ivy, the plant, (Toxicodendron radicans) is native to North America and is a member of the Sumac or Cashew Family (Anacardiaceae).  Apparently mangoes are in this family as well.  Neat.  Anyways, the genus name is derived from the greek words "toxikos" (poison) and "dendron" (tree).  Poison Ivy is an aggressive plant, easily overtaking disturbed areas such as right-of-ways, fence rows, old forest roads, vacant lots, etc.  I am currently removing poison ivy seedlings from my garden every week or so (I've recently cleared out new garden space along an old, rotting fence row by my apartment).  And, of course, you can always find it in the woods-proper.  I wish I had taken photos of the seas of poison ivy I've seen blanketing woods in southern Missouri.

So how do you identify this irritating plant?

Firstly, poison ivy is not necessarily going to be a vine (climbing and/or crawling), it can also take on the form of a small upright plant or a rediculously large, irritating shrub.

Poison Ivy in the form of 5 foot shrubbery was pretty common at Cuivre River State Park

Secondly, look at the leaves!  I'm sure you've heard the old saying "leaves of three, let them be".  Poison Ivy does have three leaves, or should I say three leaflets.  Each individual poison ivy leaf is composed of three leaflets.  Note the general appearance of the leaflets, the amount of "toothiness" can vary from plant to plant, but the poison ivy "gez" (read gestalt) is an easy one to pick up.

POISON IVY!

Pretty simple so far, but poison ivy isn't the only plant commonly encountered in the woods or elsewhere that has three leaflets.  Lets get more detailed.  One great way to hone in on poison ivy leaves is the presence of a noticeably long-ish petiole (more precisely, petiolule) attached to the terminal leaflet.

The center leaflet is cut off at the bottom of the frame, notice the long petiolule

This character is easily seen in poison ivy and the absence of this character is easily seen in a very similar looking plant (also in the Sumac/Cashew Family) known as Aromatic Sumac (Rhus aromatica).  And yes, these two plants can be seen growing right next to each other quite frequently.

Aromatic Sumac - notice how the center leaflet tapers to its base but does not feature a long petiolule

Poison Ivy and Aromatic Sumac, can you pick out both?

There are a couple more characters that set aromatic sumac apart.  For instance, if you crush up the leaves, they smell very good.  I wouldn't try this until you are comfortable differentiating this plant from poison ivy.  Also, the sumac flowers in the spring and (in my area at least) by the time poison ivy is out in force and starting to flower, aromatic sumac already has bright red, fuzzy berries.  Poison ivy berries will be greenish, fading to a whitish gray as they mature, never red.

Aromatic Sumac berries are red, Poison Ivy has white berries

There are a couple other look-alikes.  As long as you are looking closely, they are easy to tell apart.
Check out Boxelder (Acer negundo) and Virginia Creeper (Parthenocissus quinquefolia).  Both of these plants are pretty common and both could be mistaken for poison ivy to someone who isn't trained in the fine art of Poison Ivy Detection (PID).  First of all, Boxelder is a maple.  I know I've shown you that poison ivy can get to be a pretty large shrub, but if you find yourself examining suspect poison ivy that has a very large trunk, it is probably Boxelder.  Or maybe it is a poison ivy vine drooping from a tree.  Either way, it is the very young Boxelder trees that can be mistaken for poison ivy.

Box Elder - poison ivy-like but notice the extra leaflets (5 total) and pinnate arrangement

 Virginia Creeper is in the Grape Family and  is an extremely common, aggressive vine.  The leaflets of creeper can look very poison ivy-esque.  The important thing here is that creeper has five leaflets.  I have seen young creeper plants with leaves of three leaflets, but you can typically find more than three leaflets on most of the plant's leaves.  Poison Ivy never  has more than three leaflets. 

Virginia Creeper foliage, notice the 5 leaflets arranged palmately

Poison Ivy?  Nope, Virginia Creeper, see the additional leaflets on the young leaf in the left of the photo

Did I mention that you can find Virginia Creeper and Poison Ivy growing together pretty commonly?

Poison Ivy and Virginia Creeper

Lastly, you aren't necessarily safe from poison ivy just because it hasn't leafed out yet.  One of the worst cases I ever got was a couple of very early Springs ago.  I must have had some serious contact with a vine.
SO, you should know how to identify poison ivy vines as well.   Don't worry, its easy.  Poison Ivy vines have a "hairy" appearance due to the fine aerial rootlets that help anchor the plant to the tree, fence, etc.

"Hairy rope, don't be a dope!"  Poison Ivy vines running up a maple with Virginia Creeper leaves in the frame

I hope this information proves useful to you.  Poison Ivy really is easy to identify once you know what to look for.  I've heard lots of people say that they "just don't go into the woods because they'll get poison ivy every time".  It may be abundant, but it is also easy to avoid if you are paying attention.  What you really need to be leery about are those Dutchman's Breetches...

I've got some itchin' to do.