A Field Guide to the Plants of Arizona by Anne Orth Epple (1997, Paperback, Reprint)

This is the most current book for the identification of plants in Arizona. It takes a little different approach to the identification of plants than I have seen before - that being identifying plants by their flower color,, rather than by family or ecosystem etc. It has wonderful pictures which will in fact work to identify most plants in Arizona. It does present interesting descriptions of the various families and then pretty detailed descriptions of the various species of plants. I enjoyed and appreciated the descriptions of where the photos were taken and the time of year. The description of the ecosystems pretty much follows the somewhat dated Merriam System but serves for the general understanding of altitudinal differentiation. I bought the book on ebay because I could get it cheaper than at a bookstore.
If you are interested in learning about the plants of Arizona this is an excellent resource.

Excellent reference for Identifying native Arizona plants. I have bought 5 of these so far for my co-workers