Cunningham's Encyclopedia of Magical Herbs by Scott Cunningham
From Scott Cunningham: "In ancient times, plants were gods and goddesses; spirits and magicians lived within gnarled oaks and whispered from flowers. Our ancestors discovered the forces present in plants and harnesses them to improve their lives. Today, the weeds and wildflowers that grace our cities and wildernesses, the ornamental and food plants in our gardens, and even common house plants still possess incredible powers."
Scott Cunningham, known worldwide for his books on Wicca and Witchcraft, wrote this encyclopedia to help you make use of those plant powers. Overall, the book is a great reference for beginners and experienced practitioners alike.