The Great Smoky Mountains National Park occupies a massive 210 836 ha (814 sq mls) on the Tennessee/North Carolina borders, where the spectacular rugged conifer-clothed peaks rise to 1830 m (6000 ft). The lichens of the Park were rated as “completely known” in 1983, with just 301 species; and as “91–99% known” in 2008 when the total had reached 463 species. How wrong those assessments were. Just four short trips over three years by the authors, and also ‘Bill’ Buck, all exceptionally skilled lichenologists, resulted in 3,500 collections – and the species total rocketed to 770 species (plus 34 lichenicolous fungi). The addition of 330 lichenized species represents a rise of a staggering 70 % (73 % if the lichenicolous species are included) over that of the 2008 compilation. This total places the Park more than 100 species ahead of the closest other US National Park, the Klondike with 668 species. Yet can the Park now be considered “well-known” in the sense of now having a complete lichen inventory? Evidently not, as each trip added a substantial number of species not seen before, and that graph continued to rise with no indication of reaching a plateau. It was also noteworthy that an analysis of the species collected by each of the four revealed a remarkably low degree of similarity. This may be attributed to a combination of small-scale habitat heterogeneity and specialists focusing on different groups or substrata. There is a lesson here for all undertaking lichen site inventories; make several visits and if at all possible bring along several experienced colleagues.

This beautifully produced book is really three works in one: a checklist, observations on new and interesting species, and keys to the species. Preparation of the checklist has been meticulous, involving the revision of numerous previous collections from the area and also literature reports. The checklist is presented alphabetically with synonyms in the sequence and cross-referenced, and there is also a surprisingly long list of species which have been incorrectly identified by previous workers. The current status of the 22 species described as new from the Park by Degelius in 1941 is singled out for separate analysis; three survive unchanged, four are now placed in other genera, nine are placed as synonyms of other species, and six require further study.

In the second broad category, twelve species and two genera are first described as new to science, all crustose apart from one which was lichenicolous. Some of the new species are fresh collections, but others are introduced because names were found to have been misapplied or confused in North America, notably Arthonia susa (for A. taediosa auct. Am.) and Lecanora nothocaesiella (confused with Lepraria caesiella). The new generic name Kephartia in Lecideaceae is introduced for two species; it recalls Clauzadea and has Porpidia-type asci, but has violet and orange pigments in the apothecia that react purple and violet with potassium hydroxide and the ascospores lack a “halo”. Micareopsis, in Ramalinaceae, is introduced for a single Micarea-like species with a micareoid algal partner but Lecanora-type asci; it also has hyphae turning blue with potassium iodide solution, and produces sphaerophorin. It is unfortunate that no molecular sequence data were obtained to support the recognition of these genera and their placement. No less than 191 critical and insightful notes on other species then follow. Hidden amongst these is the resurrection of two generic segregates from Pertusaria (with poriform ascomata): Varicellaria (for the Pertusaria velata group), and Variolaria (with disciform ascomatata, for Pertusaria amara etc.). It has been known for more than a decade that molecular data could be used to support such splits, but others have been content to maintain a broad usage of Pertusaria; it will be interesting to see if other lichenologists follow these proposals (which necessitated some new combinations, also made here). All the new species, and some of the notes, are illustrated by fine macro- and microscopic photographs, mostly in colour.

In view of the large number of species in the Park, it is not surprising that individual species entries are foregone. The series of nine keys, however, are a major achievement and will be of tremendous asset to all working with North American lichens, particularly for crustose species. The lichenicolous species are not keyed out, because their study on the Park is viewed as “in its infancy”, but a table of those recorded by host is provided. The divisions in the couplets are generally clear, but are confined to diagnostic features and generally lack information on precise habitats, localities, and frequency – no doubt as a result of space restrictions. A considerable amount of space could, however, have been saved if an indented format had not been adopted, but full page width utilized.

The authors are to be congratulated on bringing this work to completion, in such a meticulous way, and for simultaneously demonstrating how much there is to know in even “well-known” areas of North America. This book deserves to sit on the shelves of all working with North American lichens – at least until a comprehensive modern treatment becomes available.