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The lichen genus Cladonia includes some of the very common ground cover plants in the United States and Canada. Before the compiling of this volume, the published results of research carried out with respect to this lichen genus were widely scattered, in many different languages, and often very difficult to locate or translate. This manual is an extensive compilation of the available information necessary for the identification of the members of Cladonia in North America. The compendium includes a section on the recently developed microchemical approach to the taxonomy of the group, and in order to illustrate the microchemistry of the genus a new series of photographs was taken especially for the book. One of the most important components of the volume is the key. Until now, no such key embodying the recent concepts of the taxonomy of the genus and incorporating all the North American species has been available, although there have been excellent regional keys. As a working key and manual to the lichen genus Cladonia on the American continent north of Mexico, this study will be a valuable aid to professional lichenologists, botanists, mycologists, plant ecologists, plant ecologists and naturalists.