Going off on a bit a tangent, It appears it is possible to make a plant into a Familiar, ala Familiar plants?.
And Living talismans suggests it is possible to turn a living plant into a Talisman. Though I understand that the Magi of Hermes book is not universally accepted as fully canon compatible.
Still, assuming that it is possible to turn a plant into either a Talisman or a Familiar, I keep wondering about turning a full grown tree (eg Oak) into either a Talisman or a Familiar.
Naturally this needs to be done in a laboratory, which means either moving the tree into the laboratory, or building a laboratory around the tree.
But if you manage to do that, just imagine the effects that you could enchant into the tree Familiar/Talisman - Free the Standing Tree ReHe30, and/or Stir the Slumbering Tree MuHe(Me) 25.
If the "Lord of the Rings" books have taught us anything, you want an Ent on your side during a Wizard War.