Sphagnum specialist Dierk Michaelis documents the worldwide known peat moss species (genus Sphagnum) and presents keys for their identification. This is the updated, supplemented English language version of the author's original peat moss flora of 2011 (in German), the first overall presentation of Sphagnum since Carl Warnstorf's "Sphagnologia Universalis" of 1911. Compared to the German edition, 12 species have been added, 23 new plates were added, the chapters on phylogeny and research history have been revised and a new chapter on Sphagnum ecology has been added.
Since Warnstorf's comprehensive work, numerous names have been recognized and revised as synonyms - particularly by Andrews, Eddy and Isoviita. These revisions, and the approximately 150 new species described since then, have been incorporated into this volume, as well as the results of the author's own studies. Genetic characteristics were used to define the species of problematic groups. The peat mosses are of key ecological and economic importance among the mosses. They populate almost all continents with a clear focus on northern South America, North America, East and North Asia and Europe.
The genus Sphagnum is very isolated within the Bryopsida, similarities in the construction of the sporophyte indicate a distant relation to the rockmosses (class Andreaeopsida).
For the internal classification of Sphagnum there are very different approaches with up to 4 subgenera and up to 18 possible sections, of which 14 are distinguished in this volume.
Peat mosses in the narrow sense (genus Sphagnum) feature a combination of leaf dimorphism (stem and branch leaves), cell dimorphism (living chlorophyll and empty hyaline cells) and branch dimorphism (strongly assimilating spreading branches and hanging branches serving the outer water supply) that is unique among mosses. Although the assignment of any peat moss to the genus Sphagnum usually does not cause any problems, the determination down to the species level causes difficulties sometimes.
The author introduces and describes the anatomy and morphology of Sphagnum, and explains the reproductive biology, the research history and phylogenesis of peat mosses. The systematic part is divided into three segments:
Description and identification of the sections, keys for all peat moss species, separated by continents, as well as Sphagnum species lists for 20 phytogeographic regions of the world.
The keys for Africa, Europe and North America are based on existing data and were revised and supplemented with the help of recent descriptions, updated species concepts and new floristic data. Completely new keys have been developed for South America and Asia, as these did not exist pr1eviously. 292 peat moss species are described in detail, supplemented by data on habitats, geographical distribution and lists of synonyms.
This section is supplemented by the presentation of the inner and outer characteristics on 219 plates. A very extensive bibliography rounds off the volume.

A "heavy" book on the world’s Sphagna

Firstly, let me define what I mean by "heavy" in this context. This book is big and heavy in terms of size but also in relation to its contents. It is not a field guide. The book is approximately 32 x 24 cm and weighs 2 kg!

It includes the detailed descriptions of 292 species, with supplementary data on habitats, geographical distributions and lists of synonyms. The book is divisible into 14 sections, with a key in each section, as well as for all Sphagnum species, separated by continents; in addition there are species’ lists for 20 phytogeographical regions of research history have been revised and a new chapter on Sphagnum ecology has been added.

I like the book which is very well written. It starts with an introductory section which comprises six chapters with 16 pages, gradually introducing the reader to the subject.

Next is the key to the sections which is followed by the identification keys and regional species’ lists. The descriptions of species constitute the main section of the book (280 pages) and towards the end of the book, there is a glossary, references, a list of journals and monograph series, illustration credits and an index.

Within this type of book. the index is a central feature, enabling the reader to check, for example, how the different species have been described previously. The synonyms provided at the start of all species’ descriptions are important, as Sphagnum species vary considerably, according to the habitat conditions in which they are growing; the same species may have been described as a new species or a subspecies previously.

The book is printed in black and white, with 219 drawn plates, taken either from the original publications or drawn by the author. The only colour photograph is on the cover (S. pulchrum) which is a very beautiful species, with straight leaf rows on its pending branches. Although the photograph is clear with typical individuals of S. pulchrum, it lacks the glamour of this species.

I compared the species’ list of Europe with that of Laine et al. (2018) which concentrated on European Sphagna. Michaelis notes 54 species while Laine et al. note 60 species. The difference was primarily due to the new species, described by Flatberg. In the section, Sphagnum, the new information relating to the status of S. magellanicum is not included in the keys or the species’ lists. This means that S. divinum and S. medium are not featured. Michaelis notes these changes in the text but states that at this stage he could not support a separation of these taxa, on the basis of the given morphological differences. In addition, in the section Cuspidata, three species described by Flatberg are missing: S. brevifolium, S. isoviitae and S. viride. Their taxonomic status is treated in different ways in different moss flora. Michaelis clearly describes the confusing history of these species in his text.

Dierk Michaelis’ book is an excellent continuation of the series “Bibliotheca Botanica” the first volume of which was published as early as 1886. “The Sphagnum Species of the World” is recommended for anyone interested in this fascinating, ecologically important but complicated bryophyte genus. Congratulations, well done!

Harri Vasander Department of Forest Sciences University of Helsinki, Finland

Peatlands International 4.2020