poison oak

*DOES NOT*
grow in michigan

It is commonly stated that "poison oak" grows in Michigan.  It does not.
 

Not only is there no poison oak growing in Michigan, there isn't any poison oak growing anywhere near Michigan, as per the USDA, BONAP, and Michigan Flora (which is to say no trained botanist has ever confirmed its existence here).

Let's look at established facts: There are seven species is Toxicodendron occurring in North America, with two of these species being referred to as "poison oak":

Pacific poison oak (Toxicodendron diversilobum) grows on the west coast.
Atlantic poison oak (Toxicodendron pubescens) grows in the southeast.

https://plants.usda.gov/home/plantProfile?symbol=TOXIC

I think we can entirely rule out the likelihood of Pacific poison oak growing in Michigan.  Here are better pictures of distribution maps for Toxicodendron pubescens...

plants.usda.gov/home/plantProfile?symbol=TOPU2            bonap.net/MapGallery/State/Toxicodendron pubescens.png

One certainly might look at these maps, note the presence of Altlantic poison oak in Illinois, and then conclude that it's not unreasonable that its range might extend into Michigan... but the closest Altlantic poison oak grows to Michigan is in VERY southern Illinois, bordering Kentucky (or maybe, depending on where you live, West Virginia or Maryland is closer).  But it's really far away.

plants.usda.gov/home/plantProfile?symbol=TOPU2

So, why does this "Poison oak grows in Michigan" myth persist?" 

I think it's because people learn very general (and therefore inadequate) "rules" for differentiating the two: "Poison ivy has pointed leaflets, and poison oak has rounded leaflets."  Sure.  Kind of.  But:

You CANNOT identify poison oak looking at leaflet shape alone. I’ve literally seen both pointed and rounded leaflet shapes growing out of one vine, which makes it hard for them to be different species.

Jon Sachs has a superb page on Atlantic poison oak, which includes numerous pictures of its highly variable leaflet shape (which, to thicken the plot, can include pointy leaflets).  Importantly, it also offers this key identification characteristic:

"This is about the only real way for most of us to know if we are looking at Atlantic poison oak rather than eastern poison ivy: the berries are fuzzy!" (jim adds: at least when young...)

https://www.poison-ivy.org/atlantic-poison-oak

Jon Sachs also has superb distribution maps for the poisons ivy, sumach and oak...
 

compiled from images on www.poison-ivy.org

Just a side note: Michigan Flora's page on western poison ivy, Toxicodendron rydbergii, does not present the same distribution as the map shown above...

But although fuzzy (pubescent) berries can be a distinguishing factor to identify poison oak, if you want to have a botanically solid ID, here's a key to Toxicodendrons in the south from the Flora of the Carolinas, Virginia and Georgia, which includes all 3 species we have growing in Michigan, plus Atlantic poison oak:

http://www.herbarium.unc.edu/Flora062005/Part2.pdf
 

So, there ya go.

I am always open to being wrong/learning more, so if you can botanically verify actual Toxicodendron pubescens growing in Michigan, do send me (and, more importantly, the folks at Michigan Flora) your documentation.

© jim mcdonald