Bryology: modern research and the ways forward
A special Joint Meeting of the British Bryological Society and the Linnean Society was held in the rooms of the Linnean Society, Burlington House, on 7 May 1987. This meeting, which was part of the bi-centenary programme of the Linnean Society, took the form of a symposium under the general title: “Bryology: Modern Research and the Ways Forward”. This left the organisers a very wide choice in the matter of whom to invite as speakers, the implication being that the subject matter might span the whole field of modern bryological research.
In the event the eight contributions were divided by subject matter into three sessions : “Biochemistry and cytology”, “Geographical distribution of Bryophytes” (each with three papers), and finally (after tea) a session on “Bryophyte interrelationships”, with two papers. The Chairmen for the three sessions were, respectively, Mr G. Bloom, President of the BS, Professor R.M. Schuster and Professor W.G. Chaloner, President of the Linnean Society. The symposium was attended by some sixty members of the BBS, a sprinkling of Fellows of the Linnean Society and a few visitors.
Biochemistry and Cytology
The session on Biochemistry and Cytology gave members an insight into three distinct subjects in which research is being actively pursued at the present time. Professor D.H. Lewis, of Sheffield University, took as his title “Whence and whither the bryophytes?”. Through such a title he was admitting that, whilst his research lay in the field of phytochemistry, he was interested in gaining answers to evolutionary questions. Thus, on the broad question of the links between the Hepaticae and ‘lower’ groups of organisms, Professor Lewis was able to provide phytochemical evidence for a link with the Phaeophyceae. While there were many differences, phytochemically, between brown and green algae, brown algae and liverworts had important features in common.
Turning to evolution within the Jungermanniales, Professor Lewis alluded in some detail to the work of Dr Alison Christie (on sugar alcohols) and explained how chemotaxonomic findings fitted in well with conclusions reached by taxonomists on the basis of morphological evidence. The Geocalycaceae, for example, did not comprise a natural group on the basis of their phytochemistry.
Professor Lewis also touched on the role of boron in vascular plant nutrition and evolution. It was not known to what extent bryophytes needed this element. Bryophytes did not appear to be on the direct route to the vascular plants. Throughout his paper, which drew upon a considerable body of recent research in phytochemistry, Professor Lewis’s main concern was with the value of phytochemical discoveries as an ancillary tool in evolutionary enquiry.
Professor D.J. Cove, of Leeds University, spoke next under the title “An insight into growth regulation and development of bryophytes”. He spoke on behalf of himself and Dr N.W. Ashton and reported recent and current work with which they were both involved. He explained that what he had to say would be concerned mainly with knowledge derived from studies of a single moss species, Physcomitrella patens.
He considered normal development of the germinating spore, through chloronema and caulonema stages, and the establishment of the roles of auxin and cytokinin through the study of mutants. He went on to deal with the role of light. The importance of auxin in effecting the onset of caulonema was emphasised.
Professor Cove concluded by reporting some recent attempts to look into the molecular basis of the developmental controls he had described. A way ahead could be seen clearly, involving the identification of DNA sequences and specific gene isolation. It was thus possible to look forward to an era in which “molecular bryology” would be firmly established.
Dr Martha Newton’s paper, third and last in this morning session, was entitled “Chromosomes as indicators of bryophyte reproductive performance”. It gave the views of the experienced cytologist who is in close touch with the huge volume of recent and contemporary work in bryophyte cytology.
Dr Newton reminded her audience of the value for the cytogeneticist of the 56 per cent of mosses which showed n = 2x = 10 to 14, ie. the gametophyte generation already carried a double chromosome complement. She thought the 87 per cent of liverworts which showed n = 8, 9 or 10 may well be ‘basic diploids’ too.
While stressing that polyploidy afforded the only cytological means of exploring the way in which genetic variation may become established, Dr Newton also drew attention to cases in which morphological similarity was accompanied by cytological diversity (as in Pellia) and the equally baffling examples (eg. Mylia) where the reverse was true.
For studies that would provide clear evidence of outcrossing, the importance of the provision of cytological markers (for example, by means of Giemsa C – banding) was emphasised. Illustrative examples came from the genera Pellia and Plagiochila. In this and other ways cytological findings impinged on the conclusions of taxonomists.
‘Spreading’ techniques, for the extraction of synaptonemal complexes, were seen as holding high promise for the future further elucidation of chiasmata. Only just beginning in bryophytes, but full of promise, was the molecular probing of DNA. With such techniques as these available, Dr Newton looked forward to a bright future for those researching in the cytology of bryophytes.
Geographical distribution of Bryophytes
The early afternoon session began with a paper by Professor W.B. Schofield, of the University of British Columbia, entitled “Bryophyte disjunction in the Northern Hemisphere”. Approximately 70 per cent of the European bryophyte flora, Professor Schofield pointed out, occurred also in North America, but among these could be found groups of species which displayed two well known types of disjunction. (1) the amphi-atlantic species and (2) those species found in Western Europe and turning up again only in Western North America. Once established, both these disjunctive distribution patterns are maintained through the operation of topographical and climatic factors.
Professor Schofield split the first type of disjunction into four subdivisions, to include, respectively, those species that were predominantly northern or arctic, oceanic, southern or widespread generally. He cited numerous examples of each. In the Western Europe – Western North American disjunction he again recognised four subdivisions. These were climatically based, and consisted of species referable to arctic or subalpine, oceanic, Mediterranean and steppe climatic groups. While he could cite ample examples of all four, Professor Schofield’s longest list comprised those of oceanic climates. The lecture was illustrated with a profusion of distribution maps.
By way of explanation, it was necessary to postulate inter-connections in the distant past between areas now widely separated. Both principal groups of disjuncts contained a high proportion of species which appeared to be relicts from Tertiary times. Long-distance dispersal was not thought to have occurred on any considerable scale. The interesting point was made that, whereas many Eastern North American species had a neo-tropical affinity, the link for a fair number of Western North American species lay with the Old World tropics.
Puzzling disjunctions between Western Europe and Western North America of the oceanic type might have to be explained by referring back to a “Laurasian” continent which antedated the formation of the Atlantic Ocean. While the fossil bryophyte record was too scanty to help much, there was evidence that many present-day genera of Jungermanniales have existed at least since Tertiary times.
On the whole, Professor Schofield showed himself to be well aware of the difficulty of finding fully satisfactory explanations for both major types of disjunction. He was, however, able to end on a fairly optimistic note, with his reference to improved techniques for the exploration and documentation of distribution patterns. The use of computers cannot be over-estimated, he said, and we could look forward to international co-operation on an ever-increasing scale.
Dr G. A. M. Scott, of the University of Melbourne, presented a paper entitled “Australasian bryogeography, fact, fiction and fantasy”. He began by adopting a strongly sceptical attitude towards the findings of phytogeographers. The actual history of past events was simply too incompletely known. He indicated how present-day disjunct distribution patterns could be explicable by disruptive phenomena, or long range dispersal, or a combination of the two.
Dr Scott stressed how incomplete and how rapidly changing is our picture of present-day distribution patterns. Numerous striking illustrations were taken from the Australasian bryophyte flora. He underlined the great length of time which bryophytes had had to change and modify their distributions.
The problem posed by bryophytes showing a bipolar distribution was considered, as were the exceptionally baffling distributions of Echinodium and Gigaspermum. Contraction from a previous wider distribution seemed the only explanation of today’s distribution of Takakia.
It was emphasised how easily overlooked very minute bryophytes can be. A memorable example given by Dr Scott was that of some 30 species of Fossombronia, all new to science and supposedly endemic in the Australian semi-arid, often known from just one locality and even then irregular in their appearances.
Two most interesting points were made regarding the differences, phytogeographically, between bryophytes and angiosperms. Thus, whereas the bryophyte floras of cool-temperate rain forest in Victoria and Tasmania were closely similar to those of comparable habitats in New Zealand, the angiosperm floras were widely different. Secondly, because bryophytes had existed on earth for so much longer than angiosperms (with many present-day genera and some species having been in existence in Permian times), there was vastly more time for their distributions to become modified, either by growth alone, or through distribution by propagules or from other causes.
Dr Scott summed up by saying, with reference to his chosen title, that the “facts” were the recorded presence of species in specific areas, together with the firm information we had regarding Continental Drift and the various glaciations with their associated climatic changes. The “fictions” were the recorded absences, some of which were significant, others meaningless. The “fantasy” of his title alluded to some kinds of quantitative information, especially that referring to the incidence of endemism. This he expanded to show how the term endemism had been used in a confusing manner to include four quite different phenomena.
Dr R.E. Longton, of Reading University, adopted a very different approach. He spoke on the “Adaptations and Strategies of Polar bryophytes”. He saw an important ‘way forward’ as lying in the synthesis of data from many different areas of enquiry. Dr Longton’s principal concern in this paper was with the physiological adaptations of those bryophytes which had come to live successfully in the Arctic or the Antarctic. However, he indicated that the special features of the physiology of these plants differed only in degree from those found in bryophytes generally.
He distinguished between (a) species that were widespread also in temperate and subarctic lands and (b) a much smaller group of genuinely endemic Arctic species suspected of relatively recent, possibly Pleistocene origin. Most of the more restricted element of the Antarctic bryophyte flora was thought to be composed of post-glacial immigrants from the Magellanic region.
Field experimental work has shown that mosses are capable of responding positively to favourable environmental conditions wherever these occur. The effects of freeze-thaw cycles, desiccation and continuous illumination, as potential threats to bryophyte survival, were rigorously examined.
Dr Longton pointed out that sporophyte production occurs in less than 30 per cent of the species of cool-Arctic sites in Northern Ellesmere Island, in some 10 per cent of species in the cold-Antarctic and none at all in the frigid-Antarctic.
Arctic endemics, thought to be of recent origin, tended to be monoecious and highly fertile, examples among mosses being found in the family Splachnaceae, in the genus Funaria and among the high-polyploid species of Bryum.
Drawing on his own wide experience, in both the Arctic and Antarctic, and on the research of others, Dr Longton was concerned to stress the value of physiological studies, carried out both in the field and in the laboratory, for a better understanding of the facts of bryophyte distribution.
The two papers of the third session came under the ‘umbrella’ heading of ‘Bryophyte Interrelationships’. The first was given by Professor R. M. Schuster, of the University of Massachusetts. It was entitled “The aims and achievements of bryophyte taxonomists”. In this highly stimulating address a taxonomic and evolutionary hepaticologist of unrivalled experience was concerned to draw attention to some of the salient difficulties that currently beset his subject. A big problem sprang from the application of a priority rule that inadvertently shielded the activities in ‘species making’ of past workers such as Colenso, Stephani, Kindberg and others. Out of 32 “new species” of Schistochila described by Colenso from New Zealand 31 were synonyms and of the approximately 1450 taxa currently listed under Lejeunea probably not more than 145 are valid species. A second difficulty, in the opinion of Professor Schuster, lay in the overemphasis of what are in reality comparatively trivial nomenclatural problems.
Great stress was laid on adopting a biological approach to problems of genera and species and on the importance of field studies, especially in the bryologically underworked parts of the world. Working in the tropics or the Antipodes “broadened the mind of a bryologist wonderfully”!. Thus, some of Buch’s genera of hepatics were valid for Finland, but not when South American and New Zealand species were taken into account.
Professor Schuster’s views on important questions of present-day taxonomic procedure were underpinned by detailed reference to a series of relevant examples. These consisted of well known genera (eg. Anthelia, Frullania, Pellia, Marchantia) in which exceptional difficulty was being experienced in species delimitation. In striving after a solution to such problems, the taxonomist would have to take into account cytology, tectonics, plant geography, phytochemistry and so on. For “total reliance on herbarium specimens” was “the road to disaster”.
Dealing briefly with the delineation of ‘higher categories’, Professor Schuster cited the case of the Order Metzgeriales. Here some 26 to 28 genera had been grouped quite arbitrarily in four families. In reality the order was ancient and heterogeneous and there was a great need for clarification.
Ranging widely over his subject, Professor Schuster certainly did not minimise the problems confronting us today. Yet he was able to be reasonably optimistic about the future. He foresaw ever larger contributions coming from biochemistry, cytogenetics and other disciplines far removed from classical taxonomy.
Lastly, the paper on “Cell and molecular biology of bryophytes: ultimate limits to the resolution of Phylogenetic problems” (by Duckett and K.S. Renzaglia) was presented by Professor J.G. Duckett of Queen Mary College.
Professor Duckett saw the elucidation of bryophyte interrelationships as a jigsaw in which one is always finding new pieces. There had been a decline of interest in the phylogeny of land plants because of a lack of new data. The application of cladistics to old information was futile. His own concern was with the impact of cell biology. We might, however, very well be witnessing the epitaph of this, since the future would lie more and more with nucleic acid sequencing.
The exploratory phase in ultrastructural work had shown that there was no simplicity in bryophytes at the ultrastructural level; for the bryophytes lacked no major organelles.
The comparative phase had embraced a wide range of studies of ultrastructural features in the three big groups of bryophytes. The results (of studies of blepharoplasts, thylakoid architecture etc.) had been to accentuate the lack of direct relationship between hornworts, liverworts and mosses. Professor Duckett saw “some future mileage” in the study of oil bodies, which hitherto had presented considerable technical difficulties.
Thirdly, the developmental phase in cell biology took account of such matters as the differentiation of spore mother cells and the maturation of male gametes. Again there were significant differences between the three groups.
These various studies threw some light on bryophyte ancestry and suggested a possible link with Charalean green algae, but a direct ancestral lineage from this group of algae appeared unlikely. Ultrastructural investigations tended to place the bryophytes near the algae but remote from vascular plants.
Professor Duckett considered cytoskeletal proteins such as actin and tubulin, EM studies of gametophyte-sporophyte junctions and other topics, emphasising that the brightest future lay with the elucidation of DNA sequences. He thought ultrastructural attributes should be more widely used in bryophyte Systematics, but did not see their use overturning current schemes of classification or phylogeny.
If one attempts to review, or indeed to summarise, the eight contributions collectively, one arrives at a few general conclusions. The ‘umbrella’ title was “Bryology: modern research and the ways forward”, yet it is difficult to avoid the conclusion that many people interested in observing and recording bryophytes would have found much of what was said quite outside their experience and, in places, beyond their comprehension. This stricture would not have applied to those speakers who were primarily concerned with phytogeography and classical taxonomy. These were the papers of Schofield, Scott, Longton and Schuster, where to a great extent each speaker was in turn concerned to throw new light on old concepts.
Very different was the content of the other four contributions. It could be said that they shared an interest in the excessively minute. The attention of these four speakers was focused, increasingly, on what could be seen under the highest power of the light microscope, down through the size categories revealed by electron microscopy, to the molecular level. They were thus dealing with objects and structures that were quite outside the experience of ordinary people; and these ‘ordinary people’ would include a high proportion of British field bryologists. What these investigators (Lewis, Cove, Newton, Duckett) had to say was of so specialised a character as to be fully meaningful only to others working in the speaker’s own field. All tended to reflect very strongly the prevailing influences that have been at work in shaping bryological research over the past thirty to forty years, namely the advent and subsequent advance of electron microscopy and wholly new techniques in th e broad field of biochemistry. The result has been a veritable explosion of papers, in the last twenty years, on both the ultrastructure and the phytochemistry of bryophytes.
It would have been clear to anyone attending this symposium that “modern research” in bryology carried considerable emphasis on the very minute; and “the ways forward”, for several speakers, implied peering into a future when ideas would come to be dominated by our knowledge of events at the molecular level. In these circumstances it would seem to have been of the utmost importance to allow adequate time for questions, explanations and a discussion of the implications of what had been said. No such discussion time was in fact forthcoming. An opportunity to insert it just before the tea break was unaccountably lost. Questions from the Chairman (Professor Chaloner) and Dr S.W. Greene were put to R.M. Schuster at the end of his address (allowing Professor Schuster to interpose the memorable comment that “taxonomy was a Stone Age Science”) but, after all eight papers had been delivered, no time for general discussion proved practicable. This omission, which nowadays tends to be the rule rather than the exception, is a serious one. It can lead so easily to the impression that each speaker has been operating very much within the confines of his or her own ‘compartment’, or research area, in a highly technical language fully comprehensible only to those at work in the same field, so that there is altogether too little ‘overspill’ of these important advances on to the ‘bryological public’ at large. Only generous amounts of discussion time could have provided this.
While a fair sprinkling of BBS members had come to London for this special occasion, attendance by Fellows of the Linnean Society who were not themselves bryologists appeared to be very thin. In view of the highly technical content of most of the contributions this was perhaps not altogether surprising. For unless one is familiar in a general way with most of the organisms discussed then new knowledge about them can convey little meaning; and only practising bryologists would have this familiarity. In a sense it could be said, of the symposium as a whole, that it was strong on the analytical side but – with certain notable exceptions – weak on synthesis.
“The ways forward” for ordinary field bryologists at work in Britain, or for that matter elsewhere, may not be so very different from the paths they have followed over the past quarter of a century. In brief, they are likely to remain enmeshed in problems of distribution; and inevitably, hand in hand with these will go problems relating to the definition of taxa. In this latter concern they are likely to find themselves calling upon new knowledge gained by geneticists, biochemists and electron microscopists at the ultrastructural level, but only to a limited extent. Their primary concern, in their day-to-day bryological work, will remain with what can be seen with the naked eye, hand lens and light microscope.
Several of the speakers on this occasion saw an application of their findings in the solution of problems of interrelationships at the broadest possible level – bryophyte origins, putative links with algal ancestors, connections, close or distant, between major groups of mosses or liverworts, and so on. Yet sometimes these questions were only hinted at, or touched on very lightly; and in no case was a body of evidence derived from new knowledge in the fields of ultrastructure and phytochemistry weighed in the balance against the evidence that has been gleaned from comparative morphology over a period of more than a hundred years. Where reference was made at all to such knowledge it was mainly of a vaguely disparaging nature. The implication was that it had little validity today. In brief, bryologists had to a great extent lost interest in it.
Whether or not one agrees with this attitude – with its inference that only the newly acquired nuggets of information are of genuine interest – it is instructive to look back, for a moment, and enquire what would have been the nature and content of a symposium such as this had it been held 60 years ago. True, bryogeography could easily have been well to the fore (Herzog having published his Geographie der Moose in 1926) and ecology of bryophytes, with the papers of W. Watson and others, was starting to attract serious attention. Bryophyte cytology was definitely beginning to appear ‘on the map’ (cf. early contributions by von Wettstein, M. Wilson, Heitz et al. ). The big emphasis, however, would have been on morphological evidence of interrelationships and the conflicting claims of the antithetic and homologous theories of the alternation of generations as seen in the bryophytes.
It seems likely that, 60 years ago, at least half the papers offered would have been concerned with this and related topics, and the bulk of the illustrations would have taken the form of slides made from photomicrographs giving details of the development of gametangia and young sporophytes; for herein, it was felt at the time, lay the secrets that could lead to the solution of such problems. It was an approach that chimed in well with the work of the immensely influential F.O. Bower on the pteridophytes. Francis Cavers had not practised bryology actively for nearly twenty years, but his “Interrelationships of the Bryophyta” still exerted a big influence. D.H. Campbell’s strictly morphological comparative treatment carried weight and his “Mosses and Ferns“, by then in its third edition, would have been the textbook of the day.
Now, 60 years on, quite different branches of bryology make first claim on our attention, a situation made abundantly clear by the choice of topics on the present occasion. Such morphology as is discussed consists of ‘micromorphology’, ie. the structural peculiarities shown by chromosomes and a range of organelles in different groups of bryophytes. But is it fitting that the characters provided by the ‘old morphology’ should be brushed aside so completely as they commonly tend to be nowadays?. Novel findings are always exciting but, perhaps, in the choice of criteria on which to base one’s views on interrelationships, the pendulum has swung too far. Some, at least, among older bryologists must feel this to be so.