Mission to Lichens

Photo by Marty Horowitz 

Anyone interested in looking into lichens? Specifically, what's up with these distinctly different colors?
To help you on your mission, if you choose to accept it, Debbie Bird sends this info:

Some of us were discussing the cryptogamic soil on our Tuesday Nature Walk. It was particularly noticeable after the weekend rain. There is a really nice FREE field guide to biological soil crusts that includes some keys to common lichens, and keys to some of the common mosses. Might be a lot more than you want to know, but well worth perusing. You can download it at the following site, www.soilcrust.org , it’s about 16 mb PDF. You might be able to click on the link below and get it. I didn’t print it out as it’s 104 pages, mostly keys, but the information is well worth looking over.

A Field Guide to Biological Soil Crusts of Western U.S. Drylands: Common Lichens and Bryophytes

By Roger Rosentreter, Ph.D., Matthew Bowker, Ph.D., Jayne Belnap, Ph.D. [16mb PDF file]