Plants of the Gods: Their Sacred, Healing, and Hallucinogenic Powers by Richard Evans Schultes, Albert Hofmann, and Christian Rätsch is one of the books I consider to be a "must have" when looking into religious traditions and herbalism.

I have a lot of respect for the quality of research that when into the book because it includes a great deal of the taxonomy and safety information that I expect from a book that explores what can be potentially life threatening herbalism.