The Collaborative International Dictionary of English v.0.48:

Prickly ash \Prickly ash\ (Bot.),
   1. A prickly shrub (Xanthoxylum Americanum) with yellowish
      flowers appearing with the leaves; also called toothache
      tree. All parts of the plant are pungent and aromatic.
      The southern species is Xanthoxylum Carolinianum.
      --Gray.
      [1913 Webster]

   2. (Bot.), Hercules'-club, also called the Angelica tree.
      [PJC]