Odd, colourful organisms often confused with plants

Nothing comparable with this gorgeously illustrated work exists. In spite of its "North America" appellation, this spectacular tome will serve as standard in the worldwide field of lichenology for the next two centuries, or until the final demise of all books. Not only is it a comprehensive guide to virtually all lichen genera and species on the continent but the cosmopolitan nature of lichen cover and the transcendent beauty of the plates make the work of passionate interest to field naturalists, botanists, symbiosis biologists and hobbyists beyond the borders of Canada, Mexico and the US.

The lichen body (crustose, foliose or fruticose), the nature of its reproduction (sexual or not), its propagules (asci, blastidia, isidia, soredia) and their dispersal, the unique chemistry (over 600 compounds, many limited to lichens, include depsides, depsidones, anthraquinones, puvinic acid derivatives) are explained, so that the concepts of these erudite scholars are made clear.

The reader is provided tools and standardised range maps to identify more than 800 species. The glossary and other explanations - of lichen colouration, physiology, "substrates" (the rocks, barks and other materials on which lichens grow), and of lichens as a pollution indicator, source of dyes, medicine and poison - all are exemplary. The book provides advice on names, collection and study techniques and gives a clear and comprehensive guide to the lichen species themselves.

The old insult - "this entire 828-page masterpiece is Schwendenerist!" - may be justifiably slung at all 1,700 plus photographs and drawings.

In 1869, the Swiss botanist S. Schwendener opened himself to ridicule and ignominy by suggesting that lichens were not plants at all. By 1937, botanist K. A. Timiryazev was able to defend Schwendener's conclusion. Lichens are individualised symbiotic composites of photobionts (oxygenic photoautotrophs such as cyanobacteria or green algae) with mycobionts (heterotrophic fungi, usually ascomycota). He wrote: "If I am not mistaken this curious subject has hardly been mentioned in our popular literature; nevertheless, it must be considered one of the most striking and unexpected discoveries of biological science of the last quarter century."

Microbiology, ultrastructure, biochemistry and molecular biology unambiguously support the unappreciated Schwendener.

The authors remind us that lichens, nearly all of the 3,600 North American and perhaps 15,000 species worldwide, are polyphyletic, ie, they evolved separately: "Every recognisable lichen is derived from a different species of lichenised fungus". Detailed data support this generalisation. Only when they claim that lichens "cannot be placed within the hierarchical systems of biological classification... kingdom, phylum, class... because they are dual organisms and each of the components has its own classification", do I disagree.

Like all other nucleated forms of life, lichen species can be named and classified. Indeed all visible organisms - plants, animals, protoctists and fungi (including lichens) - are at least dual composites. Furthermore, most evolved from triple, quadruple and higher-order symbiotic associations.

Polyphyly is more apparent in lichens than in other symbiotic associations. Lichens exemplify the details of complex individuality, the relations between syntrophic metabolism and morphogenesis in the emergence of novelty through physical association is made obvious in these colourful creatures, and so too the contribution of symbiogenesis to speciation and taxonomy in them is manifest.

These valiant authors, who flaunt a wealth of detail, inadvertently illustrate fundamental biological principles worthy of Schwendener's legacy. But I trust their beautiful book will not suffer his fate. I recommend it, a gift of world-class scholarship, without reservation. At its current artificially low price, all libraries, private and public, with even a remote interest in natural history, should obtain it now.

Lynn Margulis is professor in the department of geosciences, University of Massachusetts, Amherst, US.