This volume has been long awaited by me because it deals with that problematical British species ‘Caloplaca arnoldii’, and certainly provides a way forward. To begin, the Caloplaca saxicola group is re-circumscribed here, based on gross- and micro- morphology. Approximately 650 specimens were examined, including type material. Almost all the taxa are apparently restricted to the Northern Hemisphere, particularly from Europe and the Mediterranean. Many of us recognise the lobate Caloplaca as being formerly subgenus Gasparrinia, but this work excludes a significant number of well-known species such as C. aurantia, C. granulosa, etc. In fact, it needs a very close read to determine exactly what the author means by the Caloplaca saxicola group. To get an idea, it is easier to peruse the list of accepted taxa. The name C. saxicola (syn. C. murorum) is proposed as a nomen conservandum.
The group is delimited to include C. arnoldii (syn. C. saxicola subsp. biatorinoides Clauzade & Cl. Roux), C. arnoldii subsp. clauzadeana (new), C. arnoldii subsp. nana (new), C. arnoldii subsp. obliterata (new), C. arnoldiiconfusa (new), C. biatorina, C. decipiens, C. pseudofulgensia (new), C. pusulla, C. rouxii (new, syn. C. saxicola subsp. miniata (Hoffm.) Clauzade & Cl. Roux), C. saxicola and C. schistidii. None of this newly circumscribed Caloplaca saxicola group bears isidia and only C. decipiens has soredia.
Excluded are C. cirrochroa, C. saxicola subsp. laceratula, C. obliterans and C. proteus. Also excluded are occasionally lobate species such as C. gloriae, C. granulosa, C. littorea, C. marina, C. microthallina, C. necator, C. scopularis, C. tenuata, C. tenuatula and C. verruculifera.
Caloplaca arnoldii subsp. obliterata Gaya (new) is given for the taxon previously known in Britain as C. arnoldii. However, Gaya admits that there are many problems still to solve in this group. Consequently, five morphotypes on siliceous substrata are recognised and illustrated in colour photographs, and are certainly found in Britain.
Gaya writes ‘Caloplaca can be considered one of the most complex and diversified genera among the crustose lichens’. The genus is estimated by different authors to contain from 350 to over 1000 published species names. The strong similarity of lobed Caloplaca with lobed genera such as Xanthoria and Fulgensia make the delimitation of the genus problematic. Gaya recognises the C. saxicola group to have ellipsoid ascospores with median septa over 3μm thick. This would include the C. aurantia group and others within the former subgenus Gasparrinia. However, Gaya mentions, but does not review, molecular work which shows many Gasparrinia species to be polyphyletic. Hence she restricts the C. saxicola group as being one of a more natural origin. For details and discussion the reader is referred to other publications.
The methodology used in the study is well described but no details or discussions of molecular phylogeny are given. A large proportion of the book is given over to a statistical analysis of ascospore sizes. Thirty samples of each taxon were measured and 10 pages of analysis are given at the back of the book. But when mean ascospore sizes are so difficult to separate without statistical tests, the user is faced with the issue of precisely repeating the sampling and performing significance tests in order to arrive at a species identification. It seems to me that these measurements and associated tests need to be relegated to ‘supplementary details’ while the user needs to be pointed to other, more easily observed characters. The problem shows up in the keys where couplets have overlapping size ranges. In many places where sizes overlap the length/breadth ratio is given as diagnostic. There is also a difficulty when making such fine measurements, of deciding which ascospores to measure in view of their age and maturity. This degree of subjectivism seems to undermine the advantages of statistical tests.
The introductory section on morphology is nine pages long and is quite general, relating to Caloplaca as a whole. This is helpful as it discusses taxa well outside the formal circumscription of C. saxicola. However, this wide-ranging descriptive section stimulates questions on a large number of unsolved issues, such as what is a lobe and when is it not a crust? (especially the relationship between C. saxicola and C. ruderum), how do lobes differentiate from an impermanent prothallus (esp. C. arnoldii morphotypes), and so on. There is obviously considerable scope for further research on morphology and development here. The taxonomic descriptions follow the accepted format of morphology, distribution, ecology, material examined, etc., but there are no maps. The descriptions are quite detailed, especially in the discussions. Most useful is the inclusion of many lobate taxa not formally within C. saxicola. This gives the book a wider appeal. However, these ‘out-of-range’ taxa are not included in the keys. A most useful list of around 150 references occupies eight pages.
To close, this volume is a fine example of a concise but admirably detailed taxonomic treatment as we have come to expect from Bibliotheca Lichenologica. The author has done a fine job of thoroughly describing and illustrating some difficult and often confusing species. I look forward to future comparable treatments of lobate and non-lobate Caloplaca.
