The Devil is a big character in Irish folklore and some folk trads around plants exist to find him and make deals with him.
For example if you find a double rooted briar/black berry bush and go under the thing at midnight you might make a deal with the devil for whatever you wanted… in return for your soul. One story popular with Cuairdeoirs is the card player that put his deck under the briar and made the deal. Winning all over the country and donating money to good people to avoid the inevitable end.
The Elder tree is another eeeevilll one. If you burn the tree the devil will appear to you though this time usually to cause havok because youve damaged his favorite plant. Its so eeeevil that if you make a cradle from it the baby will die and if you try to herd cattle with it they will start producing bloody milk!