World Tree, generally an ash, more correctly identified in later times as a Yew. The word Yggdrasil means literally "gallow" or "horse" of Ygg (i.e., Odin).
Readers, please enjoy this guest blog post by Sandra Kynes, author of several books, including The Herb Gardener's Essential Guide, Plant Magic, and the new Witches' Encyclopedia of Magical Plants, among many others.
Although a few old books...