For most amateur lichenologists and probably many professional lichenologists, the genus Caloplaca (in the old sense) presents difficulties with identification of species. The wider genus is so large (700 recognized species) that world revision would be a daunting task. Several authors have made inroads into revising sections and many new genera have been proposed aiming at breaking up the old monolithic genus into a more manageable, understandable and natural structure. Included with the 127 existing genera, these new genera do not seem to have given much help to the amateur with the overall problem of identification. The authors are rightly concerned that those identifying Caloplaca specimens may be tempted to look up images on the internet, where so many lichen images are not correctly identified.

Therefore, Felix Schumm and Andre Aptroot have collaborated in trying to assist identification by providing a pictorial account of as many specimens in herbaria as they can lay their hands on, using not type specimens but recent material to show the characteristics of the species at their best. For each species, there are images of the specimen(s) and of the microscopical details. All the specimens are cited and with some very variable species, more than one specimen is illustrated. Not all the known species are included because recent material of the rarer worldwide species is difficult, if not impossible, to obtain. However, those species we are most likely to come across are illustrated. The photographs and micrographs are very good quality: sharp, clear and with good colour reproduction and scale bars.

The book is aimed at ‘non-specialists’ rather than the ‘3 to 4 world specialists’ of Caloplaca s. l. and is meant to complement other published information of particular groups and regional floras where fuller descriptions are available, including ecological and taxonomic information and discussion. The taxonomic literature may or may not be available to us all, depending on our own collection of literature and access to library resources.

The aim is laudable and the authors should be congratulated for the effort they have put into this work – some work! With 4 volumes having a total of 2700 pages and weighing 4.5 kg, this is a monumental publication. I have only seen an electronic copy but I assume the real book is of a similar standard and style as Schumm's earlier books which will be well known to many readers. It may be one of the best resources for Caloplaca s. l. identification in the world but the question is how well do the authors meet their aims and how useful will this book actually be?

Any work on Caloplaca s. l. will be huge and to be useful this presents problems with cost. Marketed at 400 Euros for the hardback, it might seem beyond the affordability of most amateur lichenologists but Amazon's digital edition for just over half that price may be less of an outlay. Size also presents problems of access to the information in a comparative way. To help this there is a short key to groups of species, including those not represented, but which species these are is unfortunately not indicated in the key. The species in this book are arranged in alphabetical order and there is an index to all the species and well-known synonyms listed under Caloplaca and the various other genera within Caloplaca s. l., so one should be able to find a desired account fairly quickly. The emphasis is that this book is meant to supplement other literature which may or may not be available to us all. Let us hope that it will encourage us to attempt Caloplaca identification and help us especially with those species which need more critical examination.