OK, Lots to respond to, and lots to take in. This Board is GREAT!
The active compound in asprin is salysillic acid. It's found a lot in nature. Willow, Slippery Elm, you can even relieve the pain of a tooth ache by squashing a ladybug into the problem area!
Other than oils, there are a few other things to look out for. Lots of fruit trees contain cyanide compounds. Sometimes they are in certain tissues and not others. I would have said to avoid apple, but evidently you just need to peel off the bark! Smart Ross! Pom fruits and stone fruits are some that do contain cyanide, but maybe only in seeds or live bark?
I think I see a common thread. Most conifers seem to accommodate orchids. Could it be the pH?
Buddlia? I never would have thought of using this for a mount! I have weaved a crude hanging basket from thinner butterfly bush branches, but it wasn't that sturdy. I'll have to try this!