My post isn't showing up on the forums :( I'm going to add a comment to see if that causes it to show up.

My guess would be buckthorn or pin cherry. Do the fruits have a stone? It is not a serviceberry.

Sadly, I agree that it is Rhamnus cathartica. Really tough invasive to get rid of. They laugh at being cut to the ground. I've read a great article (with positive results) on the non-chemical removal means they note in this data sheet: https://files.dnr.state.mn.us/natural_resources/invasives/terrestrialplants/woodyplants/buckthorn_what_you_should_know.pdf

The first two in your list (first sentence of original post) do not have the paired leaves and the leaf vein pattern of the buck-thorn.

Ron, are you saying its not European buckthorn?

One thing I've noticed with buckthorn is that the wood is yellow.

https://www.ontario.ca/page/pin-cherry

Another vote for Buckthorn. The paired veins in the leaves are typical of Rhamnus; I don't see the glands on the leaf petioles I'd expect to see on a Prunus species; and the Pin Cherry description says the fruits are bright red and the original poster says they are black/purple.

Rhamnus cathartica at Virginia Tech Dendrology

WW

My first feeling was buckthorn also, but I'm wondering if there are 2 species in one spot?

I studied the plant a little more carefully and found that there is a single thorn at the tip of each branch. Also the fruits contain three or four seeds each, so it seems the buckthorn ID is right. I appreciate everyone's responses. I guess it's time to start trimming.