In the tranquil setting of Wye College, Kent, members met to discuss some of the most interesting aspects of bryology today. An emphasis on taxonomy demonstrated the continuing role of herbaria and the innovation of axenic cultivation and scanning electron microscopy in consolidating the firm basis on which all other research depends. Not only did we see in two papers the kinds of problems posed by little known and, in some cases, seriously threatened tropical floras but we also saw greater precision brought to bear at the infra-specific and generic levels, respectively, in two others as a result of sophisticated modern techniques. Work of this sort has rendered the British bryophyte flora one of the most well-known and one that is thus amenable to the detailed recording and mapping described by another speaker. It is similar taxonomic work, moreover, which has provided a framework for the subtle eco-physiological probing of growth and distribution shown by two other speakers to be of profound importance in current and future considerations. Summaries of these papers are provided below. With a reporter from the wider scientific press in our midst, however, the meeting has also been brought to a more general audience (New Scientist, 1582, p. 25, 1987).
Miss A. J. Davidson (University of Reading) “Aspects of bryophyte herbivory.”
Many invertebrates live, oviposit or pupate in the shelter of bryophyte colonies, but bryophytes are thought seldom to be freely consumed by either vertebrate or invertebrate herbivores. Rates of decomposition are also low leading to accumulation of bryophytes as humus or peat. Literature reports suggest that sporophytes may be more commonly eaten than gametophytes. These comments are conjectural, however, as there have been few detailed studies of bryophyte consumption. An investigation is therefore being conducted with the objective of providing definitive information on this point and providing information on the nature of any deterrent that may be involved. Preliminary results are presented here.
The generalist herbivore chosen for this study were slugs in the family Arionidae. Superficially, moss communities provide an ideal environment for slugs. They are moist and protective and readily apparent to ground living animals. There are few previous observations on moss consumption by gastropods.
The palatability of mosses to the slugs Arion hortensis Fér., Arion rufus L. and Arion subfuscus Draparnaud was investigated by comparing the consumption of five moss species Mnium hornum, Atrichum undulatum, Polytrichum commune, Funaria hygrometrica and Brachythecium rutabulum with that of two flowering plants, lettuce, Lactuca sativa L. and Dandelion, Taraxacum officinale L., in laboratory feeding trials. Young leaves of Lactuca were the preferred food type. Taraxacum was also eaten in substantial amounts, but consumption of moss shoots was negligible, except for small quantities of Funaria in some feeding trials. Slugs were then offered stages in the moss life cycle: Mnium, Brachythecium and Funaria at 1. Protonemata; 2. Leafy shoot; 3. Immature capsule (capsule expanded and green, calyptra fallen); 4. Mature capsule (capsule brown, but operculum intact). A . rufus and A. subfuscus showed a clear preference for immature capsules or protonemata to other tissues in all three moss species tested.
Casual observations in the field support the contention that moss shoots are not commonly grazed. Types of damage found include leaf lamina holes (usually with vein and where present border cells left intact) and a loss of apical leaves and stem. Several herbivores causing leaf holes have been identified as dipteran and microlepidopteran larvae and very occasionally slugs. Leaf fragments of Mnium, Brachythecium and Polytrichum have been found in rabbit pellets indicating that rabbits may be responsible for removing some moss shoot apices. However, moss leaf fragments formed no more than 5% of the total plant material identified.
Conversely, there is abundant evidence of immature capsule damage in many moss species. A. rufus and A. subfuscus have frequently been observed consuming immature capsules in the field. Results of a permanent quadrat assessment of capsule damage suggest that only about 25% of Mnium hornum and less than 20% of Brachythecium rutabulum capsules survived to dehiscence at the sites sampled. Thus where feeding does occur spore output is considerably reduced.
Available evidence thus indicates that mosses are only vulnerable to slugs at certain short-lived stages in their life cycle. Possible reasons for this poor utilisation of bryophyte biomass include low nutrient value, a physical resistance presented by the cell wall or a chemical defence involving secondary metabolites.
In all mosses sampled the average ash-free calorific value obtained for the immature capsule was similar to or slightly lower than the value obtained for the leafy shoot. Mnium hornum mature capsules had a slightly higher energy content (18.79 KJg–¹) than immature capsules (18.65 KJg–¹). Thus, there appears to be no energetic advantage to be gained by eating the immature capsule. However, it must be recognised that potential energy yield and metabolizable energy yield are not the same. Rumen content studies (Thomas & Edmonds, 1983; White & Trudell, 1980) suggest that moss leaves are poorly metabolized. A preliminary examination of slug faeces supports this theory. Possible reasons for low digestibility include a concentration of holocellulose or “lignin like” material within the cell wall or the presence of tannins or other polyphenolics.
These factors are being investigated by comparing the phenolic component of the moss shoot and immature capsule and by presenting moss extracts to the slugs on artificial substrates. First results indicate that slugs prefer a moss cell extract to the whole fresh shoot suggesting that the moss cell wall provides the barrier to free consumption. Whether this barrier is a physical obstruction or a chemical interaction with the digestion of the consumer remains to be determined.
Thomas, D.C. & J. Edmonds (1983). Rumen contents and habitat selection of Peary Caribou in winter, Canadian Arctic Archipelago. Arct. Alp. Res. 15: 97-105.
White, R.G. & J. Trudell (1980). Habitat preference and forage consumption by reindeer and caribou near Altasook, Alaska. Arct. Alp. Res. 12: 511-529.
Mr A. Eddy (British Museum, Nat. Hist.): “Malesian Leucobryaceae”.
Mr T. Ellis (British Museum, Nat. Hist.): “Taxonomic problems in the Calymperaceae.”
The Calymperaceae is a pan-tropical family of largely epiphytic, acrocarpous mosses characterised by the possession of leaves with a sharply defined hyaline, semi-sheathing base and marginal or intra-marginal ribs. Fusiform gemmae are frequently produced from the costa, most often in a mass radiating from the apex.
Calymperes and Syrrhopodon are the largest constituent genera. In Calymperes the capsule is eperistomate and enclosed by a persistent calyptra, spore release being effected through longitudinal splits in the latter. Gemmiferous leaves are often highly modified, especially at the apex. The nature of this apical modification is slightly different in each species and is therefore an important feature in classification.
In Syrrhopodon the capsules have a haplolepidous peristome and a fugacious calyptra, and, in most species, there is little differentiation of the gemmiferous leaves. The generally recognised subgenera differ widely and the genus is therefore considered to be polyphyletic.
Fleischer (1904) observed a Syrrhopodon-like peristome in various genera (Arthrocormus, Exodictyon (including the recently segregated Exostratum), Leucophanes and Octoblepharum) with leaves resembling those of Leucobryum. Accordingly he transferred these from the Leucobryaceae into a new family, the Leucophanaceae, which he grouped with the Calymperaceae. Prior to Fleischer’s work it had become generally accepted that all mosses with leucobryoid leaves were derived from a ingle ancestor. As the peristome in Leucobryum (the most widely known of the genera with leucobryoid leaves) resembles that of Dicranum and its allies, it was assumed that this ancestor was shared with the Dicranaceae.
The features of dicranoid and Syrrhopodon-like peristomes described by Edwards (1979), together with evidence gathered from the examination of leaves lend support to Fleischer’s classification. The leaves of all the genera in the Leucophanaceae possess features that, to some extent, can be related to the basic calymperoid leaf form. In Exostratum they are the least modified from this calymperoid form and resemble most closely those of Syrrhopodon.
Andrews (1947) first advocated placing the Leucophanaceae into the Calymperaceae. He suggested a connection between Leucophanes and Syrrhopodon subgenus Leucophanella on the basis of a supposed homology between the hyalocysts of the two groups, their peristome structure and gemmae. However, the hyalocysts in Leucophanella form part of the lamina while most in Leucophanes are part of the costa and are therefore not homologous.
Costal hyalocysts similar in form to those of Exostratum (but independently evolved) do occur in the Calymperaceae and their presence is often associated with the production of gemmae. This association is less obvious in Calymperes subgenus Somphoneuron as the species of this, probably polyphyletic, subgenus possess gemmiferous and non-gemmiferous leaves with a costa largely composed of (apparently non-porose) hyaline cells.
It is possible to view the present leaf morphology of the genera in the Leucophanaceae as being the result of reduction and modification from the leaf-form of an ancestor which they share with the modern Calymperaceae. In the course of this process these genera have evolved porose, costal hyalocysts independently of those of the dicranaceous leucobryoid mosses. Therefore, agreeing in spirit, if not in detail, with the recommendations of Andrews (1947) and the various proposals of subsequent authors, the genera of the Leucophanaceae have been formally transferred to the family Calymperaceae as the subfamily Leucophanoideae (Ellis, 1985).
Andrew. A. L. (1947). Taxonomic Notes VI. The Leucobryaceae. Bryologist, 50, 319-326.
Edwards, S. R. (1979). Taxonomic implications of cell patterns in haplolepidous moss peristomes. In: Clarke, G. C. S. and Duckett, J. G. (eds.), Bryophyte Systematics. Academic Press, London, pp. 317-346.
Ellis, L. T. (1985). A taxonomic revision of Exodictyon Card. (Musci: Calymperaceae). Lindbergia 11: 9-37.
Fleischer, M. (1904). Die Musci, der Flora von Buitenzorg. Band 1. E.J. Brill, Leiden.
Dr M.C.F. Proctor (University of Exeter): “Scanning electron microscopy and some thoughts on Polytrichadelphus“
Mr R. C. stern (Chichester) and Dr F. Rose (Liss, Hants): “Bryophyte distribution in Sussex – the progress on the new Sussex bryophyte flora.”
Sussex is a good area for bryophytes with about 470 taxa. It has a long coastline and a low level of air pollution. It has varied topography (up to 919 ft) and rainfall (from 25 ins to the upper 30’s). The main reason for the diversity, however, is the varied geology.
The West Sussex coastal plain has recent deposits including gravels; old pits have rare species such as Fossombronia husnotii, F. incurva and Atrichum angustatum. Near the sea are the epiphytes Cololejeunea minutissima and Ulota phyllantha, as well as Leptodon smithii which also occurs on walls. The last is one of the “southern” species as is also Pleurochaete squarrosa which occurs on chalk grassland.
The South Downs provide some of the most interesting species on open grassland such as Entodon orthocarpus, Porella arboris-vitae and Scapania aspera. In the wooded areas on chalk stones are Seligeria paucifolia and Tortella inflexa.
The Lower Greensand is well represented in West Sussex with some of both wet and dry heathland, on which species such as Odontoschisma denudatum and Dicranum spurium occur. On the wooded hills, especially on chestnut coppice areas, there are other Dicranum species including montanum, tauricum and flagellare.
The Weald Clay areas are well wooded with abundant epiphytes such as Lejeunea cavifolia, Neckera pumila and Zygodon baumgartneri; on clay banks there is Ctenidium molluscum “woodland taxon” which needs to be described as a separate species.
This last also occurs on the High Weald which comprises the Hastings Beds – a complex series of clays and sands with some very fine and celebrated sandrock areas. These are noted for the occurrence of “Atlantic” species such as Hyocomium armoricum, Harpanthus scutatus, Pallavicinia lyellii, Orthodontium gracile and many other species, particularly of hepatics. At the eastern end of East Sussex is Fairlight Glen with Fissidens rivularis, Tortula freibergii and Dumortiera hirsuta.
With the assistance of Mr H. W. Matcham, a bryophyte atlas is in course of preparation. Maps will be on a 10 km square basis, or by tetrads for the less common species. It is hoped to publish this in 1990.
Mr C. Studholme (University of Manchester): “The peroxidase activity and isozyme variation of Sphagnum cuspidatum from polluted and unpolluted areas”.
The occurrence of ecotypes of higher plant species tolerant of sulphur dioxide is a well established phenomenon, but their counterparts in the Bryophyta are virtually unknown. Although variation in susceptibility to sulphur dioxide is observable between different bryophyte species in much the same way as it is in higher plants, the far greater sensitivity of bryophytes as a whole may mask any intraspecific variation which might exist.
The opportunity to examine whether such variation in susceptibility to sulphur dioxide pollution is present in bryophytes is available in the southern Pennine uplands. The long pollution history of this region has resulted in dramatic changes in the hydrology and vegetation of the blanket bogs and the ombrotrophic Sphagnum communities, once widespread, have been replaced by a far less diverse flora dominated by Eriophorum vaginatum. However, situated in isolated parts of this eroded and uninteresting landscape are a few populations of Sphagnum cuspidatum which may well be relics of the once extensive Sphagnum cover. If these are relics, and thus pollution tolerant ecotypes, they should display physiological, genetic and growth differences when compared with plants from unpolluted regions.
When grown in an artificial rainwater solution amended with increasing concentrations of bisulphite (the major solution product of sulphur dioxide) the growth of Sphagnum cuspidatum from three southern Pennine populations was affected far less than was the growth of plants from three populations with no history of pollution. Furthermore, at the highest concentration (0.3 mM) severe tissue damage was visible in the plants from the three unpolluted populations, while plants from the southern Pennines remained unaffected. This was the first piece of evidence to suggest that the southern Pennine populations of Sphagnum cuspidatum might be pollution tolerant relics.
An electrophoretic study was performed on plants from the same six populations in order to determine whether southern Pennine plants were genetically different from their counterparts in unpolluted regions. An examination of over 400 samples revealed that, for peroxidase, 5 isozymes were common to all samples. At the three sites unaffected by pollution these 5 bands were supplemented by a combination of others representing up to 10 additional isozymes. In the southern Pennine populations however these supplementary bands were rare. Thus a peroxidase isozyme profile with a low number of isozymes typifies southern Pennine populations of Sphagnum cuspidatum, although such an arrangement may also be found in some plants from unpolluted populations. Whether this signifies selection for a tolerant genotype or reflects the chance establishment of more recent wind-blown propagules, which have spread vegetatively to produce the southern Penn ine populations, is uncertain.
It has been reported that the total activity of the enzyme peroxidase is at a lower constitutive level in higher plant ecotypes known to be tolerant of sulphur dioxide. The Sphagnum cuspidatum plants from the southern Pennine populations also have a lower base level of peroxidase activity which may be further evidence that the plants are tolerant ecotypes. However, while higher plants respond to sulphur dioxide with an increase in peroxidase activity, Sphagnum cuspidatum plants exhibit a depressed activity both with laboratory bisulphite treatments and when plants from unpolluted regions are transplanted to the polluted southern Pennines. This would not appear to account for the lower base level of peroxidase activity in southern Pennine plants as the base levels were determined after a long period of growth under controlled conditions in the laboratory. Similarly it is not the additional isozymes typical of populations from unpolluted regions which produce overall higher activities. The 5 main isozymes common to all samples examined stain darkly and account for a large proportion of the activity observed in the total activity assay. The activity of two of these isozymes (PER 4 and PER 5) are, however , sensitive to environmental conditions and these are consistently seen to produce dark bands in plants from unpolluted sites, but to stain poorly in plants from the southern Pennines. A drop in total enzyme activity when plants from unpolluted sites are transplanted to the southern Pennines is accompanied by a significant reduction in the stain intensity of the same two isozymes. None of the additional isozymes characteristic of plants from unpolluted populations appeared in the isozyme profile of southern Pennine plants transplanted to an unpolluted site, although stain intensity of the two isozymes PER 4 and PER 5 did increase to account for the observed increase of total enzyme activity.
The presence of isozyme variation in some populations of Sphagnum cuspidatum is an addition to the growing number of reports that bryophytes may be as genetically diverse as higher plants, but the reduction of peroxidase activity under polluted conditions reported here for a bryophyte may serve to highlight important physiological differences between the two groups.
Dr H. L. K. Whitehouse (University of Cambridge): “The use of axenic cultures to resolve the components of aggregate species in mosses”.
Growing bryophytes in agar culture provides a technique equivalent to the experimental garden long used by flowering plant taxonomists. ‘Axenic’ means ‘not contaminated’, but bacterial infection of Knop’s agar cultures of mosses seems often to favour their growth. The cultures are started in petri dishes, using any part of the moss, surface sterilized with 5% sodium hypochlorite solution. When growth starts, the material is transferred to 10 cm tubes of culture medium.
The first success of using this technique to recognise the components of aggregate species was with Bryum mildeanum Jur. Some individuals produced flat red gemmae, with a serrated edge, on the rhizoids, including those in the leaf-axils, and were found to be B. riparium Hagen. The gemmae were very abundant in the cultures. B. riparium is a brown-stemmed plant of non-calcareous habitats, particularly where water seeps over rocks at the sides of streams, and is widely distributed, though rare, in the west and north of Britain and Ireland. It also occurs in west Norway and there is a single record from North Carolina (coll. L. E. Anderson, 1949). A similar plant occurs in east Nepal (coll. W. D. Foster, 1977) and in Sikkim, but keeps distinct in culture. B. mildeanum is a red-stemmed plant, lacking gemmae, of limestone rock crevices and also of rocks in base-rich streams. It is not known in Ireland and is of very local occurrence in Brita in.
The culture method was also used to confirm the distinctness of Dicranella staphylina Whiteh. from species with which it might be confused such as D. rufescens (With.) Schimp, and D. varia (Hedw.) Schimp. D. rufescens differs from D. staphylina in many characters including Its red stems, rhizoids and tubers. D. varia has narrower leaf-cells than D. staphylina and the tubers are paler, more variable in shape and size and less constantly present – indeed, often absent, particularly from non-calcareous habitats.
Recent work in collaboration with Dr M. E. Newton has established that two taxa occur within Tortula stanfordensis Steere. Cultures on Knop’s agar of the two forms keep distinct. T. stanfordensis sensu stricto occurs widely in California and in Victoria, Australia, and is known in Europe from a single locality in the Dordogne, France, coll. J. G. Duckett, 1977, from the Severn, Wye and Usk valleys in the west of England, from west Cornwall, from the Magnesian limestone in Yorkshire and from a few scattered localities elsewhere in England, Wales, Scotland and Ireland. Almost all the populations are female only. The second taxon occurs in the Thames and Tweed basins. It differs from T. stanfordensis in having a more acute leaf apex with a larger apiculus and larger leaf cells and is autoecious, or rarely synoecious, with gymnostomous capsules on short setae produced regularly in spring. It has a chromosome number of n = 52 or, more rarely, n = 26, while T. stanfordensis has n = 13.
A study of Gymnostomum luisieri (Sergio) Sergio ex Crundw. in collaboration with Mr A. C. Crundwell, using cultures of this and allied plants, has helped to clarify the distinctions between them. G. luisieri, has been confused chiefly with G. calcareum from which it differs in its short leaves, 0.3 – 0.4 mm long, and in the frequent presence (always, in culture) of ovate or bottle-shaped gemmae in the leaf axils and on the protonema. G. calcareum lacks such gemmae and has ribbon-shaped leaves often twice as long as those of G. luisieri. In the Near East G. luisieri has been confused with G. mosis (Lor.) Jur. Milde, but that species has bistratose leaf margins and lacks the characteristic gemmae of G. luisieri. The three species keep distinct in culture. G. luisieri has a distribution that is centred in the Mediterranean area and is largely south-western in Britain and Ireland.
An offshoot of the work on Gymnostomum luisieri has been the recognition, in collaboration with Mrs J. Appleyard and Dr M. O. Hill, of the occurrence of Leptobarbula berica (De Not.) Schimp. in Britain. More recently it has been realised that L. berica has been much confused with Gyroweisia tenuis and this has led, in collaboration with Dr H.J. During, to the discovery of L. berica in the Low Countries. L. berica seems to be comparatively frequent in south-east England; the north side of churches at ground level is its favourite habitat. As would be expected, it keeps distinct from Gyroweisia tenuis in culture, although there was much confusion until it was realised that the plants growing at localities in Cambridgeshire where G. tenuis had supposedly been known for over 30 years were in fact L. berica. The perichaetial leaves of L. berica have an inflated base and taper to a sub-acute apex, w hile those of G. tenuis have a much less inflated base and a more obtuse apex. Also, the bottle-shaped gemmae on the protonema of G. tenuis are usually biseriate (2 cells wide), while those of L. berica are more slender and usually uniseriate.
It is self-evident that axenic cultures provide a powerful tool for resolving the components of aggregate species. The problem is to recognise which taxa merit such study.
Following the Annual General Meeting (Minutes in Bulletin 52), there was an evening conversazione during which a number of demonstrations, listed below, were examined. Moreover, further interest was generated by the exciting discovery of Trichostomopsis umbrosa on the college itself and of Leptobarbula berica on the church nearby. The meeting proved to be not only of great reward but also enjoyable, and for this we are deeply indebted to Dr M.A.S. Burton for volunteering such careful and imaginative arrangements.
|K.J. Adams:||BBS Library items.|
|D.G. Long:||Notes on Andreaea.|
|B.J. O’Shea:||I.A.B, software library for IBM PC compatibles.|
|P.W. Richards:||Spare reprints.|
|R. Stevenson:||Miscellanea Bryologica.|
|M.P. & H.L.K. Whitehouse:||Stereoscopic photographs of thalloid hepatics from Achill Island.|
|H.L.K. Whitehouse:||Drawings, distribution maps and a list of British records of Leptobarbula berica.|
Field meeting, 27 September 1987
The weather was perfect for the Sunday excursion. A small wood, typical of the well farmed North Downs countryside near Wye had been chosen, since it had a list of over 70 species, free access in the company of its warden John Taplin, and parking space nearby. Chalk stones in it had yielded Seligeria paucifolia, Fissidens pusillus var. tenuifolius and Tortella inflexa. The Seligeria was abundant though not in good fruit; the Fissidens was fruiting well; Tortella was scarce. The species list was available to most members who set about with a will to add to its numbers. To date 9 additions have been given to me; nothing spectacular but to me the patch of Ephemerum recurvifolium was especially pleasing since I have seen it but rarely in Kent. I thank all who have sent me records after the meeting, and especially John Taplin who prepared the species list.
Lunch was eaten at Hothfield. Hothfield bog is probably the most eastern in Britain and though bogs are commonplace in parts of the country, this one and the other at Keston (now in the London area) are our treasures. The great abundance of Polytrichum commune must have been apparent to all. Eleven species of Sphagnum were found with Odontoschisma sphagni growing among them. The 10 km card for the area holds one of Kent’s longest species lists so members could find a pleasing number to look at.
A few members went further afield and I have been sent records of Tortella inflexa and Leptobarbula berica. Again I thank members who have sent records which add to my tetrad maps of Kent bryophytes and for a pleasant day in good company.