I don't agree that an understory tree catagory would be helpful, but I can understand your interest in it.* Maybe you could do a google search with that term.
There are so few ornamental vines that grow in shade I'm not sure a separate catagory for them would be that helpful.
You can find your hardiness zone here and include it with or as your location in your profile as I've done.*
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.