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The Liverwort Flora of the British Isles
374
Book reviews / Biological Conservation 94 (2000) 273±374
The Liverwort Flora of the British Isles By Jean A. Paton; Harley Books, Colchester, 1999, 626 pp, including 314 text ®gures, hardbound, ISBN 0-946589-60-7 (hbk), £52.50 Liverworts, forming the class Marchantiopsida of the Bryophyta, are not as numerous as the more familiar mosses but of similar size. Paton's ¯ora, in common with previous liverwort ¯oras, also includes the small class Anthocerotopsida, or hornworts. There are only four hornworts in the British ¯ora so they take up little space. The remainder of the book deals with the 292 liverworts proper, so called because the thalli of one common species, Conocephalum conicum, were thought to resemble lobes of the liver. The Marchantiopsida are a remarkably variable class, comprising ®ve orders between which there is little super®cial resemblance. In addition to this ordinal diversity, there is one species that is parasitic on the fungi of tree mycorrhizae and lacks chlorophyll. There are others that contain fungi but are also chlorophyllose and leafy. A few contain colonies of cyanobacteria. Some are aquatic. One, Ricciocarpos natans, is the size of Lemna and grows with Lemna. With such remarkable diversity, it might be expected that liverwort identi®cation would be easy, so that an identi®cation manual would be simple to produce. Surprisingly, this is not so. Several genera contain dicult, closely-related species. Cephaloziella (13 spp.) is exceptionally dicult. The species are minute and not completely understood; identifying them requires ``skill and often a great deal of patience''. For these reasons and also because many liverworts have soft tissues and evanescent characters such as oil bodies, they cannot be well known without a long and arduous apprenticeship. Jean Paton has been working on liverworts for more than 40 years and has acquired a unique knowledge of the British and Irish ¯ora both in the ®eld and in the herbarium. This book, her magnum opus, has been eagerly expected and lives up to expectations triumphantly. It is a ¯ora on the grand scale, weighing 2.6 kg and with fullpage illustrations of most species. The illustrations typically show several stems and a range of variation. For example, Lophozia bicrenata, a relatively non-critical species, has illustrations of 9 fertile stems, 6 sterile stems, 10 leaf gemmae, 17 separate leaves, 6 leaf cells with contents, 2 perianth mouths, 3 leaf apices, 3 antheridial bracts with antheridia, and a stem cross-section showing enclosed fungal hyphae. One gets an immediate impression of the plant, missing only its characteristic smell, which is ``similar to cedar wood or old leather'', so that
``in the ®eld it is only necessary to crush the plants lightly for the aroma to become apparent''. Readers of this journal may wonder how much a ¯ora, even a grand ¯ora, can contribute to conservation. Species conservation depends on a good knowledge of species; it will surely be enhanced by an identi®cation manual of the ®rst quality. Conservation also depends crucially on understanding habitat requirements. Paton describes the habitat of each taxon at length and in detail, including associated species and altitudinal range. For British species, categories of threat are indicated, using the abbreviations CR critically endangered, EN endangered, VU vulnerable. Plants for which a special collecting permit is required in Great Britain are signi®ed by the code 8B, indicating that they are listed in Schedule 8 of Wildlife and Countryside Act (1981). The disadvantage of these categories is that they are local in their signi®cance. Thus Southbya nigrella, widespread in the Mediterranean region, is indicated as EN 8B, and, therefore, apparently worthy of a high degree of protection, whereas Scapania nimbosa, an uncommon mountain plant known only from Ireland, Britain, Norway, Yunnan and the Himalaya, is not. These categories are available only for Great Britain; a comparable Irish set of designations was not available. With small organisms such as bryphytes, there are serious practical problems caused by categorizing species with a code such as 8B. Marsupella profunda, for example, is so hard to identify that it is unlikely to be determined in the ®eld. What are we meant to do? Should we ignore it? Should we look for it and risk breaking the law? Ought specimens collected in ignorance to be destroyed? It remains an uncomfortable fact that many liverworts have to be checked microscopically, so that collecting is a necessity for the serious student, just as it is for beginners. Whatever our attitude to collecting, the diversity and beauty of the liverworts will continue to entrance ®eld botanists. Jean Paton's ¯ora is a true classic, an inspiration for bryologists both in this generation and for many to come.
0006-3207/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0006-3207(99)00180-9
Mark O. Hill Institute of Terrestrial Ecology Monks Wood, Abbots Ripton Huntingdon PE17 2LS, UK Tel.: +44-1487-773381 fax: +44-1487-773467 E-mail address: [email protected]
Book reviews / Biological Conservation 94 (2000) 273±374
The Liverwort Flora of the British Isles By Jean A. Paton; Harley Books, Colchester, 1999, 626 pp, including 314 text ®gures, hardbound, ISBN 0-946589-60-7 (hbk), £52.50 Liverworts, forming the class Marchantiopsida of the Bryophyta, are not as numerous as the more familiar mosses but of similar size. Paton's ¯ora, in common with previous liverwort ¯oras, also includes the small class Anthocerotopsida, or hornworts. There are only four hornworts in the British ¯ora so they take up little space. The remainder of the book deals with the 292 liverworts proper, so called because the thalli of one common species, Conocephalum conicum, were thought to resemble lobes of the liver. The Marchantiopsida are a remarkably variable class, comprising ®ve orders between which there is little super®cial resemblance. In addition to this ordinal diversity, there is one species that is parasitic on the fungi of tree mycorrhizae and lacks chlorophyll. There are others that contain fungi but are also chlorophyllose and leafy. A few contain colonies of cyanobacteria. Some are aquatic. One, Ricciocarpos natans, is the size of Lemna and grows with Lemna. With such remarkable diversity, it might be expected that liverwort identi®cation would be easy, so that an identi®cation manual would be simple to produce. Surprisingly, this is not so. Several genera contain dicult, closely-related species. Cephaloziella (13 spp.) is exceptionally dicult. The species are minute and not completely understood; identifying them requires ``skill and often a great deal of patience''. For these reasons and also because many liverworts have soft tissues and evanescent characters such as oil bodies, they cannot be well known without a long and arduous apprenticeship. Jean Paton has been working on liverworts for more than 40 years and has acquired a unique knowledge of the British and Irish ¯ora both in the ®eld and in the herbarium. This book, her magnum opus, has been eagerly expected and lives up to expectations triumphantly. It is a ¯ora on the grand scale, weighing 2.6 kg and with fullpage illustrations of most species. The illustrations typically show several stems and a range of variation. For example, Lophozia bicrenata, a relatively non-critical species, has illustrations of 9 fertile stems, 6 sterile stems, 10 leaf gemmae, 17 separate leaves, 6 leaf cells with contents, 2 perianth mouths, 3 leaf apices, 3 antheridial bracts with antheridia, and a stem cross-section showing enclosed fungal hyphae. One gets an immediate impression of the plant, missing only its characteristic smell, which is ``similar to cedar wood or old leather'', so that
``in the ®eld it is only necessary to crush the plants lightly for the aroma to become apparent''. Readers of this journal may wonder how much a ¯ora, even a grand ¯ora, can contribute to conservation. Species conservation depends on a good knowledge of species; it will surely be enhanced by an identi®cation manual of the ®rst quality. Conservation also depends crucially on understanding habitat requirements. Paton describes the habitat of each taxon at length and in detail, including associated species and altitudinal range. For British species, categories of threat are indicated, using the abbreviations CR critically endangered, EN endangered, VU vulnerable. Plants for which a special collecting permit is required in Great Britain are signi®ed by the code 8B, indicating that they are listed in Schedule 8 of Wildlife and Countryside Act (1981). The disadvantage of these categories is that they are local in their signi®cance. Thus Southbya nigrella, widespread in the Mediterranean region, is indicated as EN 8B, and, therefore, apparently worthy of a high degree of protection, whereas Scapania nimbosa, an uncommon mountain plant known only from Ireland, Britain, Norway, Yunnan and the Himalaya, is not. These categories are available only for Great Britain; a comparable Irish set of designations was not available. With small organisms such as bryphytes, there are serious practical problems caused by categorizing species with a code such as 8B. Marsupella profunda, for example, is so hard to identify that it is unlikely to be determined in the ®eld. What are we meant to do? Should we ignore it? Should we look for it and risk breaking the law? Ought specimens collected in ignorance to be destroyed? It remains an uncomfortable fact that many liverworts have to be checked microscopically, so that collecting is a necessity for the serious student, just as it is for beginners. Whatever our attitude to collecting, the diversity and beauty of the liverworts will continue to entrance ®eld botanists. Jean Paton's ¯ora is a true classic, an inspiration for bryologists both in this generation and for many to come.
0006-3207/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0006-3207(99)00180-9
Mark O. Hill Institute of Terrestrial Ecology Monks Wood, Abbots Ripton Huntingdon PE17 2LS, UK Tel.: +44-1487-773381 fax: +44-1487-773467 E-mail address: [email protected]