Meeting report

Bryological symposium

The meeting proved to be one of exceptional interest and one that was well attended. It was further distinguished by the presence of two overseas members, both of whom had agreed at short notice to contribute very informative papers before an audience of over sixty members in the palatial National Museum of Wales. Meeting as we were in the Museum and, later, in the Herbarium, it was highly appropriate that we should hear a detailed account of the activities of a herbarium in the United States of America, but the programme also covered a wide range of other aspects of bryology. An initial look at the effects of successive glaciations on the development of the British bryophyte flora was particularly pertinent to the topic of another speaker concerned with the taxonomy of Tortula in the southern hemisphere. Adaptation to environmental factors, but of quite a different kind, were also considered by those speakers who demonstrated on the one hand the physiological response of Sphagnum to nitrogen and, on the other, the nature and extent of the Greek bryophyte flora. There was also a paper which gave us the unusual opportunity not only to learn more about the hornworts, but also to do so in the context of their developmental morphology. It was a challenge to our President to draw these diverse subjects together but this he did in his presidential address. Summaries of these papers follow.

Mr M. F. V. Corley (Faringdon, Oxon.): “The bryophyte flora of the British Isles during and after the Ice Age.”

The present distribution of any species of bryophyte is a product of its dispersal mechanism and its reactions to ecological and climatic conditions, both now and in the past. The effects of historical factors on species distribution are considered here.

Conditions in Britain at the height of the last glaciation were extreme, with a considerable part of the country under ice sheets and the remainder experiencing a severe climate. Yet sub- fossil evidence and comparison with peri-glacial areas in Greenland indicate that many bryophyte species were present.

With the retreat of the ice, some of these species became extinct; many arctic-alpine species migrated northwards and up the mountains. Species of warmer climates invaded the southern parts of Britain and spread northwards. At first open habitats were plentiful and wetlands far more extensive than they are today. Calcareous soils were also more widespread than they are now. A number of fenland bryophytes are known to have been common at that time.

Changes in sea level following the melting of the ice sheets flooded land bridges to outlying islands, including Ireland, and eventually cut off the whole of Britain from mainland Europe, making colonisation by additional species more difficult. Soon afterwards, in the Atlantic period, higher rainfall and warm conditions caused forest cover to reach its greatest extent; at the same time moorland areas developed extensive peat cover. This period was optimal for the spread of species of warm shady habitats which reached their greatest extension, and have become more restricted since, often becoming confined to western coastal districts. It was also critical for fen species, with increasing acidification of fens from peat drainage water, and for species of open habitats, which were severely restricted at this time, which may explain many anomalous distributions, where species were confined to a few sites and have not spread extensively since.

Following the Atlantic period, lower temperatures and the increasing activities of man have progressively diminished the area of forest. Many species distributions are at least partly influenced by man. Indeed the greatest factor changing distributions at present is the effect of man in altering habitats.

Dr M. R. Crosby (Missouri Botanical Garden): “The I. M. S.: a muscological data base.”

Dr J. A. Lee (University of Manchester): “Nitrogen as an ecological factor in bryophyte communities.”

For many bryophyte species nitrogen deposition from the atmosphere represents the major source of combined nitrogen for growth. Ammonia is assimilated via the glutamine synthetase-glutamate synthase pathway, and nitrate-nitrogen enters this pathway following reduction to ammonia. The enzymes of nitrate reduction, nitrate and nitrite reductase, are substrate inducible and their activity can be used to assess nitrate utilization by bryophytes.

Observations in the ‘unpolluted’ environment of Swedish Lapland demonstrated how ombrotrophic Sphagnum species respond to nitrate deposition in natural rain events. Sphagnum fuscum showed a rapid induction of nitrate reductase activity to each rain event, the activity declining at the end of the event as the result of nitrate depletion. Repeated artificial addition of 1 mM nitrate to Sphagnum fuscum plants in the field resulted in progressively less induction of nitrate reductase activity after each addition because at this artificially high concentration the supply of reduced nitrogen was too high for growth requirements. The induction of nitrate reductase activity was progressively inhibited by a product of ammonium assimilation, probably glutamine concentration. These and other observations demonstrated that under ‘natural’ conditions there is a very close coupling of the metabolism of at least ombrotrophic bryophytes with the nitrogen sup ply in rain events.

During the last century there has been approximately a fourfold increase in atmospheric nitrate deposition as the result of atmospheric pollution. Observations in one of the most grossly polluted regions of Europe, the southern Pennines of England, showed that ombrotrophic Sphagnum species transplanted into the blanket mires showed rapid and massive increases in total tissue nitrogen concentration. These transplants also rapidly lost their ability to respond to nitrate deposition in rain events by induction of nitrate reductase activity. Indigenous southern Pennine Sphagnum cuspidatum plants showed very low nitrate reductase activity and did not respond to rain events. In grossly polluted areas the nitrogen supply from the atmosphere is currently supra-optimal for the growth of ombrotrophic Sphagnum species, since in addition to field observations, the concentration of nitrate and ammonium in rain reduced the growth of these species in laboratory experiments. These observations were discussed in relation to the potential effects of the increased atmospheric nitrogen supply on the ecology of bryophyte communities in general.

Dr P. J. Lightowlers (Institute of Terrestrial Ecology, Penicuik): “The Systematics of austral Tortula: unravelling southern hemisphere taxa of a temperate genus. “

Tortula is a genus whose species occur mostly in the temperate zones of both hemispheres. Although the north temperate species are well studied, the southern hemisphere species are poorly known and, as with other temperate genera, a study of the southern hemisphere species may tell us more about the phylogeny and origins of the genus as a whole.

My knowledge of southern hemisphere Tortula is the result of a taxonomic revision of the genus on the subantarctic island of South Georgia, a study I was able to extend to cover the entire subantarctic and antarctic regions. Most of the southern hemisphere, particularly southern South America, has a poorly known bryoflora: there are a large number of species described in the literature, many of which careful study will show to be synonymous. So a stable and clear nomenclature has not yet been achieved and, in general, taxonomic revisions like that produced for Tortula (Lightowlers, 1985) are necessary before any southern hemisphere bryophyte species can be properly understood.

Subantarctic Tortula species can readily be divided into hair-pointed and nonhair-pointed groups and it is the latter group which is the most diverse. Eight subantarctic species can be distinguished in this group: T. anderssonii, T. arenae, T. filaris, T. fontana, T. geheebiaeopsis, T. robusta, T. rubra and T. saxicola. Leaf and lamina cell measurements, as well as other characters, clearly separate these species. Many of them have also been grown together under identical conditions and were found to remain distinct.

In contrast to the non-hair-pointed plants, the hair-pointed group is more taxonomically difficult. Four provisional taxa were distinguished but these did not appear to be specifically distinct, a conclusion which was supported by evidence from a Principal Components Analysis. Growth experiments also suggested that at least two of the taxa were unstable in cultivation. All of the hair-pointed material was therefore referred to one species, T. princeps, which must be regarded as polymorphic (at least in the southern hemisphere). One of the four provisional taxa was treated as a separate variety (var. magellanica) but the others were combined with the var. princeps.

The non-hair-pointed species of subantarctic Tortula, with the exception of T. saxicola, have dentate or denticulate, lingulate to oblong leaves and base marginal leaf cells which are elongated, rather like a vestigial border. (One species, T. arenae, has a fully bordered leaf.) Together, these species form a coherent and apparently natural group whose closest relative in the northern hemisphere is T. subulata. Because of its bordered leaves, this species has the same leaf base areolation, it has a similar leaf shape and may have denticulate leaves (in the var. angustata). Since T. subulata is the type species of Tortula, the southern hemisphere plants are referred along with this species to the section Tortula.

1. saxicola, like T. princeps, has entire leaves and areolation at the leaf base in which the quadrate upper-lamina-type cells run down the leaf margin into the basal part of the leaf. Both species thus appear to belong to the section Rurales.

Tortula in the subantarctic is therefore dominated by the non-hair-pointed plants here referred to the section Tortula. This group appears to be mainly mesophytic and probably more primitive than the highly drought-adapted section Rurales. Section Tortula may well have originated in the southern hemisphere with large primitive species like T. robusta, and have given rise to the section Rurales through species like T. anderssonii and T. saxicola. These have morphological features intermediate between those typical of the section Tortula and those of the section Rurales.

Like Tortula, many bryophyte genera may have originated in the southern hemisphere although many may have diversified later in the northern hemisphere. A southern hemisphere origin for many bryophyte taxa is particularly likely as, at one time, most of the land masses formed part of the great southern Gondwanaland continent. Reference

Lightowlers, P. J. (1985). A synoptic flora of South Georgian mosses: Tortula. Bull. Br. Antarct. Surv. 67, 41-77.

Dr C. D. Preston (Monks Wood, Huntingdon): “The Greek bryoflora: an English view. “

The first bryophytes recorded from Greece were gathered by John Sibthorp (1785-1796). A second collection was brought from the Ionian Islands by the talented and eccentric philhellene Lord Guildford. Thereafter records accumulated gradually, most based on specimens collected by botanists primarily interested in flowering plants. It was not until the late 1950s, with increased opportunities for travel, that bryologists visited Greece regularly. Despite this recent activity, only 2 areas (Crete and Corfu) can be considered to be reasonably well-known bryologically.

The Greek bryophyte flora is intermediate in size between that of the species-rich countries of NW Europe (e.g. British Isles, Germany) and the much more species-poor Middle Eastern territories (e.g. Cyprus, Iraq, Israel). When the Greek flora is compared to the British, it is found that almost all the leafy liverworts recorded from Greece are also found in Britain but over one-third of the Greek thallose liverworts do not occur here: these include the genera Plagiochasma, Mannia, Athalamia, Corsinia and Oxymitra as well as many species of Riccia.

The potential for fieldwork in Greece was illustrated with reference to the varied habitats on the island of Samothrace in the NE Aegean.

Dr M. C. F. Proctor (Exeter University): “Amateurs, professionals and the study of bryophyte distribution.”

K. Renzaglia (East Tennessee State University): “The structure and development of hornworts.”

The anthocerotes are a structurally distinct group of bryophytes which show developmental peculiarities in all phases of their life cycle (Renzaglia 1978). The vegetative gametophyte is a simple thallus which, except for the occurrence of small epidermal cells and large internal cells in Megaceros, is composed of isodiametric cells of equal size. Large, single plastids with well-defined pyrenoids characterise the cells of most hornworts, the notable exception being Megaceros which has internal cells with up to 14 chloroplasts which lack pyrenoids (Renzaglia & Hicks, 1984). In several species of Anthoceros, Notothylas and Dendroceros, schizogenous mucilage cavities develop in the dorsal thallus while ventral mucilage clefts are found in all species. These latter structures are the site of development for the Nostoc colonies characteristic of all hornwort thalli. Scattered mucilage idioblasts, likewise, occur in most species while slime secretion from epidermal cells serves to protect the apical region and developing gametangia.

Apical growth occurs through the activity of either a wedge-shaped (most genera) or a hemidiscoid (Dendroceros) apical cell. The distinct growth form of Dendroceros, i.e., the thickened midrib and monostromatic wings, is attributable to this difference in generative cell shape. Lateral derivatives of either cell type give rise to wing tissue and the outer midrib, while the basal merophytes produce midrib tissue, rhizoids and the gametangia. Branching is a true dichotomy in which two branch apical cells are formed through an equal division of the apical cell.

Gametangia occur in rows and are sunken along the dorsal midline of the thallus. The solitary archegonia develop from an epidermal initial while the endogenous antheridia occur singly or in groups of up to 25 (Anthoceros) and are produced from a subepidermal initial. Spermatozoids, as exemplified by Phaeoceros (Moser, Duckett & Carothers, 1977; Carothers, Moser & Duckett, 1977) and Notothylas (Renzaglia & Carothers, in press), differ from those of other bryophytes in that they possess identical basal bodies which are positioned side-by-side at the anterior end of the gamete. Moreover, a spline aperture, a posterior mitochondrion and a stellate pattern in the basal body, features common in most bryophyte spermatids, are absent in the hornworts.

Developmental features of the sporophyte which emphasise the isolated nature of the group include the longitudinal first division of the zygote, the development of sporogenous tissue from the amphithecium and the continued growth of the sporophyte from a basal meristem. Diversity in mature sporophytes serves as the primary basis for the separation of the 5 or 6 genera in the group. In general, the hornworts are a homogenous plant group which when compared with other land plants show unique morphogenetic and structural features.

References

Carothers, Z. B., Moser, J. W. & Duckett, J. G. (1977). Ultrastructural studies of spermatogenesis in the Anthocerotales. II. The blepharoplast and anterior mitochondrion in Phaeoceros laevis: later development. Amer. J. Bot. 64, 1107-1116.

Moser, J. M., Duckett, J. G. & Carothers, Z. B. (1977). Ultrastructural studies of spermatogenesis in the Anthocerotales. I. The blepharoplast and anterior mitochondrion in Phaeoceros laevis: early development. Amer. J. Bot. 64, 1097-1106.

Renzaglia, K. S. (1978). A comparative morphology and developmental anatomy of Anthocerotophyta. J. Hattori Bot. Lab. 44, 31-90.

Renzaglia, K. S. & Carothers, Z. B. (in press). Ultrastructural studies of spermatogenesis in the Anthocerotales. IV. The blepharoplast and mid-stage spermatid of Notothylas. J. Hattori Bot. Lab.

Renzaglia, K. S. & Hicks, M. (1984). Megaceros in the Southern Appalachians. Assn Southeast. Biol. Bulletin 31, 78-79.

Conversazione

The Annual General Meeting which followed (Minutes in Bulletin 48) was succeeded in the evening by a conversazione and sumptuous buffet generously provided by the National Museum of Wales. A large number of demonstrations were displayed and are listed below. An outstanding feature of this meeting was the opportunity it afforded to examine the public galleries of the Museum, as well as the Herbarium which houses the B. B. S. collections. For this, we are greatly indebted to Mr A. R. Perry, whose efforts on our behalf, coupled with those of his family, were so clearly seen in the success of the meeting.

M.E. Newton

Field meeting

Sunday 22 September dawned fine and sunny after the deluge of the previous evening and this ensured a good number of members taking part in a day in the field in Glamorgan (v.c. 41). Choosing good bryological sites within easy reach of a city or exit routes for people making homeward journeys later in the day, is not always easy, and had been somewhat problematic in this case. But the three sites visited turned out to be well suited to our requirements, with some interesting finds, including four new vice-county records.

The first locality was Coed-y-bedw, west of Taff’s Well, a 40-acre deciduous woodland owned by the Glamorgan Trust for Nature Conservation. Geologically interesting, it embraces the transition zone between Coal Measures in the north and Carboniferous Limestone in the south, and possesses sandstone outcrops and limestone rocks separated by a marshy stream bed. Ninety bryophytes have been recorded and we saw such diverse elements as Sphagnum angustifolium, Rhytidiadelphus loreus, Saccogyna viticulosa, Eurhynchium schleicheri and Dicranum tauricum. But the best new finds were also new vice-county records: Trichocolea tomentella* and Campylium calcareum*.

We drove north and in the grounds of the Miners’ Rehabilitation Centre at Talygarn we had lunch during which Harold Whitehouse set to minutely examining some old oolite steps for Leptobarbula berica. Unfortunately he later decided that the plant he was collecting was probably just young Barbula vinealis. However, he and Chris Preston made up for this later by finding at the base of a wall the best material of Trichostomopsis umbrosa* either of them had seen in Britain. We spent the first part of the afternoon in the overgrown boggy woodland surrounding the two lakes at Talygarn. Here the epiphytes are quite lush with such species as Metzgeria fruticulosa in evidence, but we found nothing of great note although Cryphaea heteromalla, a very rare species in this part of the country, was on Sallows and on a sandstone coping stone. Besides these there were good growths of many common woodland species, especially useful for beginners.

Back at the cars the party split into three: those who wished to visit the final locality on the programme; those who thought it time to leave for home; and a third party lured by Harold Whitehouse to Hengrove Wood, Claverton, near Bath (6), to try to re-find Leptobarbula recorded there earlier. They refound the spot, but it was so dark, owing to shading by trees, that they could not see any bryophytes! Meanwhile, back in Glamorgan, the now very select party went to Hensol Forest in the region of Pysgodlyn Mawr (the “Large fishpond”) to examine an extensive area of sallow carr. The water level of this oligotrophic pond had recently been raised by a dam in order to create more stable conditions for the fishermen using it, and this was causing a rapid increase in the Sphagnum along one of the shorelines, not only in area, but also, it seems, in species. Here on sallows Tom Blocked detected small amounts of Colura calyptrifolia*, a most unexpected find, with its next nearest known localities being in West Cornwall and Merioneth. We wondered whether other excitements such as Drepanolejeunea hamatifolia might turn up, but we were not that fortunate!

A.R. Perry