A lichen is composed of one or more (out of tens of thousands of) species of fungi living with one or more (out of hundreds of) species of algae and possibly one (of fewer than one hundred) cyanobacterial species. Combinations of those three taxa have created characteristics that defy human-made rules for classification. It would take longer than a human lifetime to become an expert in all the species of lichens, and it would certainly take a much larger book to describe all the variable characteristics that arise from those combinations.

While thin-layer chromatography (TLC) procedures and molecular DNA studies are being used to sort out lichen relationships and lineages, they are beyond the scope of a general introductory guide. This guide is intended to help the reader begin the journey of learning about lichens based on ecological, morphological, and chemical characteristics of species found in the Southern Great Plains region.