This book, the latest in Kew's Botanical Magazine Monographs series, is without doubt an impressive compilation of information about each of the three named genera. The author is exceptionally well qualified to write it, not only on account of his many years of studying these highly ornamental small shrubs, but also because he is the International Cultivar Registrar for each of the genera (as well as Andromeda). But the book also reflects the author's main preoccupation with the historical and cultural aspects of his studies, after all who else could begin a modern book with a ‘prolegomenon'?
The title of the book is problematic: the qualification of ‘from the Northern Hemisphere’ is obviously intended to exclude the 800 or more South African species, a very few of which are borderline hardy in the milder parts of the UK. This does lead, however, to the use of the word ‘hardy’. The vast majority of the species treated are hardy, at least in the UK and, presumably, similar climates elsewhere. However the book does cover some European species which are decidedly not hardy in the UK, and certainly not in more continental climates. An example being Erica sicula of which the author notes, ‘plants presently known to me in cultivation are all housed under glass …’ While he does go some way to recognize this in the introduction, readers should treat the use of the term with some caution.
As befits a botanical monograph, the treatment is almost entirely confined to species and hybrids: a selection of the cultivars is covered in an Appendix. Each genus is dealt with separately with Calluna and its one species, but for Daboecia the author accepts two species, choosing to recognize the Azorean endemic at species level rather than as a subspecies which has been widely accepted since McClintock (1989). The author advances no new evidence to support his treatment but does provide some insight into the debates that have occurred around this issue in the past. The concept of Erica in the book includes the former genera Bruckenthalia (one species) and Pentapera (two species); the former following E. G. H. Oliver's (2000) treatment. The author accepts, therefore, 20 species in Europe and adjacent regions, including the relatively recently accepted species, Erica platycodon, and its subspecies, maderincola; as well as the debatable taxon, Erica andevalensis, first described in 1980. For the latter the author bases his decision on the unique habitat in which the species occurs and the distance from its likely closest relative. However, when dealing with the pentaperan heaths, the author has decided to reduce E. bocquetii to a subspecies of E. sicula, presenting compelling arguments for so doing. While there are possible inconsistencies with his treatment of the species, the author notes regularly that he has been hampered by the lack of conclusive molecular data on the genus to inform his decisions. This extends to the arrangement of the species. These are grouped according to morphological similarity but this does not reflect a formal infrageneric classification for, according to the author, ‘The subgeneric classification of Erica is in turmoil … a plaything for botanists who are enthralled by molecular taxonomy.’
While there are excellent descriptions provided for each of the species, supplemented with interesting notes on the distribution, ecology, ethnobotany and even cultivation, a baffling lacuna is the absence of any guide to identification, most of all a key. While it may be possible to cross-refer between descriptions and notes to species in their groups, there is no summary that allows the reader to decide to which group a species belongs.
Closer reading of the species accounts shows that there is some duplication of information, and some information that applies to more than one species, which is only noted in one place. Given that there are only 38 pages of introduction, 26 of which are an account of the genera in cultivation, it would seem that there was ample opportunity to bring together more general information on morphology both at macro- and microscopic levels, phytochemistry and ecology (additional to the notes on pp. 102–5), all of which could provide the reader with a valuable insight into the genera and species. Instances are the discussion of lignotubers in Erica on p.204, under Erica arborea, and the gland-tipped hairs in the section on cross-leaved heathers on p.235.
The book is beautifully illustrated throughout with the colour paintings by Christabel King (which are the subject of the author's prolegomenon) and Wendy Walsh, as well as the exquisite full page line drawings by Joanna Langhorne, each one drawn from a cited specimen, and others by Stella Ross-Craig. While there are plenty of photographs, these are of variable quality and a few are somewhat uninformative (e.g. Fig. 70 of Erica erigena, and Fig. 124 of E. arborea). It is also disappointing that there is not a single photograph of E. maderensis in flower. Distribution maps are provided for some species but there is no explanation of the use of a paler shade of pink in some (e.g. Fig. 169, Erica cinerea). The use of arrows to indicate small, disjunct populations can be distracting and, in the case of the map for E. ciliaris, it is evident that the Dartmoor population (mentioned in the text) has been missed out.
Errors are, however, few. One conspicuous one occurs in the account of Daboecia cantabrica, where on p.74 the basionym is given as ‘Vaccinium cantabricum (L.) Huds.’ In a previous paper (Nelson, 2000: 58) this is correctly given as Vaccinium cantabricum Huds.
In general the book is highly readable and full of fascinating information, especially some of the footnotes. It definitely fills a gap: books on heathers in horticulture are plentiful but an up to date account of the European species was badly needed and here in these 442 pages we have it. It is as authoritative as it is idiosyncratic but it will be a point of reference for many years to come.
The final illustration is the author's bookplate, and the book from which the bird appears to be issuing pages is entitled, ‘Everything you wanted to know about Heathers but were afraid to ask’. Maybe, in the end, that is the best description of this monograph.