how do you know if a tree is rare or not? and where are they?
Here is a list of them. It's under "Specific Trees".
Well, you can´t know by yourself. Check other sites to see which are those. There are about 6 rare trees in whole game. If you were talking about D/P/Pt, rare trees are yellow.
headbutt? every tree in HG/SS can be headbutt i think...