From the Preface: "...There are at least 1,170 species of mosses and 524 species of liverworts reported from North America and all have been found to be different in some significant way. This book is about these different species and how they may be separated from each other. It has been designed for the beginning student of mosses and liverworts as well as the serious amateur. Though all of the species known from North America are not included, the vast majority of common ones, and even some rare but unusual ones, are included. This edition, besides updating the taxonomic treatment of earlier editions, including major changes in organization and style, and [includes] many additional species....One hundred twelve additional species that includes 42 additional genera have been added. Most are illustrated in the 117 new figures prepared by me. A majority of these additional species come from the southeastern United States and western North America. Also, the results of many studies since the appearance of the revised edition in 1956 have necessitated over 135 name changes. A 'List of Synonyms' is included in order to aid one in associating the names used in this book with the names used in past editions or in other works on mosses and liverworts....Finally, the information for each species has been expanded to include a brief description, a discussion of habitat, and a statement about its general geographic range as reported in the literature..." - from Amzon