A checklist of Iowa lichens is presented at the same reference as the checklist of fungi. Lichens are, after all, essentially fungi that have algae living symbiotically with them. That reference is:

Tiffany, Lois H. and George Knaphus, 1998. "The Fungi. Lichens, and Mysomycetes of Iowa: A Literature Review and Evaluation." Proc. Iowa Acad. Sci. 105(2) 35-44.

There is a field guide that is available:

How to Know the Lichens, Second Edition by Mason E. Hale, publisher WM. C. Brown.

Some may find this book useful but it seems to rely extensively on chemical tests for determining what species a lichen belongs to. That sort of takes all the fun out of it for me.

There is a huge, coffee-table sized book that is a pleasure to read:

Lichens of North America, by Irwin M Brodo, Sylvia Duran Sharnoff, and Stephen Sharnoff. 2001 Yale University Press, New Haven and London.

This book is quite expensive and worth every penny.

The Ledges State Park near Boone, Iowa is one of our most popular parks.  A special interprative, self-guided lichen trail has been developed for it, and slides for it can be viewed here, or find it on the Iowa DNR web site.