The seventh edition has been revised to conform with the nomenclature of The Lichens of Great Britain and Ireland (2009) and more recent changes to the British lichen flora. lt includes many species that do not appear in that flora. It provides a description of most of the species likely to be found in Great Britain and Ireland, those excluded being very rare or very local. Mark Powell has given valuable assistance in the revision of this edition and has added a new section on lichenicolous fungi on Physcia and Xanthoria.
Entries usually consist of a description of each species, notes on habitat, the results of the simple spot tests as well as notes on distribution with a map giving 3 date separations including when it was most recently recorded. A particular feature of this book is the large number of photographs, with most species illustrated in full colour. These are supplemented by numerous line drawings of microscopic and other diagnostic features. There are frequent suggestions to assist in separating species that appear similar but could otherwise cause confusion.
The popular generic ‘lateral key’ has been retained in an enlarged form. A generic synopsis is included to assist the more experienced lichenologist.
Each genus has a key or table to the species contained in this book. Where there may be confusion, these keys often include similar species from other genera. Where genera are closely related a ‘group’ key is frequently supplied.