A plant I can easily identify

I found a most unwelcome visitor in our yard this weekend:

(in focus behind the other plant)

Poison Ivy. Nasty stuff for those who are allergic, like me.

I have found poison ivy in and near our property before, but not very often (only 4-5 times in the several years since we moved in), so I don't frequently look out for it specifically.

This past week I got an itchy rash on my arm, feet, and leg - just small areas, nothing serious. I had no idea what caused it at the time, but it looked very similar to poison ivy rash that I'm all too familiar with from past encounters. Still it didn't make sense since I hadn't been out in the yard other than mowing.

But this morning I noticed the rather large poison ivy plant in the first photo above and that confirmed it for me. I went on the hunt for more and found several others throughout the yard. In our backyard, most of the yard is very shaded and instead of mulching we just leave the leaves that fall during the fall and more or less leave it as is. Throughout the year various weeds and plants inevitably grow here. I occasionally will spray them with Round Up when they get out of control, but I don't go crazy over it as it takes quite a bit of time and herbicide to spray them all. I'm not out in that part of the yard very often, but our dog is, and I presume that is how I was somehow exposed to it.

Years ago I got a pretty bad rash in places all over my body. I unknowingly got into some and likely got it on my shoes, then my hands and/or under my fingernails, and proceeded to spread it everywhere I touched. Needless to say it wasn't fun and wasn't something that I wanted to go through again, so I proceeded to spend many hours researching it on the Internet to learn not only how to treat it, but also identify it. I forget what I ended up using to treat it (I don't remember it working particularly well), but I do remember very well how to ID it. These days it sticks out to me like a sore thumb and I can spot it very easily. I feel like this post wouldn't be complete if I didn't provide some of my tips, so here are my general identification guidelines (nothing scientific here):

1. Location. Look for it at edges of grass fields, or just into a shady area/forest, under and growing up trees that are in the open or receive some sunlight. I've also seen patches growing in unmowed overgrown areas in the middle of fields. They generally seem need some light, but not necessarily full sun (they seem to like a bit of shading). They certainly don't get anywhere near full sun where they are in our yard.
2. Leaves. Look for three leaves to a stem (generally). The leaves can be very large or small (I generally see the large leaves most frequently on vines). The leaves sometimes don't look very symmetrical and can take on various irregular shapes. The leaves are very brittle, so in a more  trafficked place look for damaged leaves.
3. When in vine form, look for external roots on the vine (looks "hairy").

That's about all I've got, I think. Some other factoids:

1. Dogs aren't allergic to it. Not all humans are allergic to it either.
2. Once a rash has broken out on the skin it has been absorbed by the body and can no longer be spread. But it can spread if it's under your fingernail, on your shoe, etc.
3. The plant has to be broken in order to be exposed to it, but as mentioned the plant is extremely brittle. I've never tested to confirm this.

Source: internet research from years ago and my own observations over the years since then.

Anyway, I sprayed all the poison ivy I found in our backyard with Round Up Poison Ivy - just regular Round Up is not enough to kill it (I tried when I first found some in our yard and it came right back). Perhaps this is more indication that there is enough light to grow supina bluegrass back there!