Annual General Meeting 1992: Chelwood Gate, Sussex

HomeEventsAnnual General Meeting 1992: Chelwood Gate, Sussex

26 September 1992 - 27 September 1992

Meeting report

Bryological symposium

A complete change from our normal venues for autumn AGM weekend meetings was provided by the University of Sussex’s pleasant field centre, the Isle of Thorns. Situated in the Ashdown Forest, also known as Winnie the Pooh country, fine weather enabled us to make the very best of the beautiful surroundings. The centre provided all that could be needed for the weekend (26-27 Septermber) including a friendly atmosphere. The standard of accommodation was high, and David Streeter’s organisation proved faultless. Francis Rose provided two interesting local excursions on the Sunday. I am also grateful to the speakers who provided a satisfying mix of topics and presentations of excellent quality. The following short summaries have been provided by the authors.

Philip Lightowlers

Prof J.G. Duckett (Queen Mary College, London), Prof. R Ligrone (University of Naples) and Drs J.A. Goode and A.D. Stead (Royal Holloway and Bedford New College, London): How things fall off bryophytes.

Loss of adhesion in the abscission regions of vascular plants, whether these be leaves, floral parts, seeds or vegetative propagules, results from hydrolysis of the middle lamellae coupled with expansion and rounding-off of the same cells. By contrast, the wide assortment of diaspores produced by bryophytes (Longton and Schuster, 1983) displays a range of abscission mechanisms paralleling those seen in the fungi and in the algae. Although used extensively in bryophyte taxonomy, until very recently (Bopp et al., 1991; Duckett & Ligrone, 1992) the development and liberation mechanisms of diaspores have been virtually ignored since Correns’ (1899) encyclopedic treatise.

Apart from fragile leaves, and caducous leaves and perianths, which become detached by breakage through an intercalary region of thin-walled living cells, other abscission mechanisms in bryophytes involve uniaxial filaments. The rhizoidal gemmae of mosses are the only examples of diaspores where an abscission mechanism (other than rotting of the subjacent cells) is lacking, a situation almost certainly related to the fact that these propagules are produced underground.

Deciduous shootlets (e.g. Leucodon), axillary bulbils (e.g. Pohlia) and cauline gemmae (e.g. Tetraphis) are liberated by the random breakage of thin-walled stalk cells. Formation of new internal walls followed by rupture of the old external walls is a feature shared by the gemmae in the liverworts Riccardia and Metzgeria and the mosses Tortula latifolia and numerous Orthotricha. Breakage along the middle lamella characterises the liberation of catenate gemmae in the Jungermanniales.

The most specialised liberation mechanisms are those involving the formation of abscission or tmema cells. These are a constant feature of the foliar gemmae in Calymperes (Ligrone et al., 1992) and Dicranoweisia cirrata, the axillary gemmae in Zygodon and Bryum flaccidum and the protonemal gemmae in Funaria and many species of Bryum (Goode et al., 1993). In the last two genera a transverse array of microtubules characterises tmema cell development. Though reminiscent of a preprophase band otherwise unknown in moss protonemata, its function is more likely exclusion of chloroplasts from the tmema cell rather than positioning of the new cell plate. An equatorial band of microtubules and actin microfilaments found in the mature tmema cells of Bryum probably has a key role in wall breakdown leading to the fragmentation of the protonema.

In old cultures, or in the presence of abscissic acid, the cylindrical chloronemal cells of most mosses de-differentiate into spherical brood cells. These contain random arrays of microtubules recalling those seen in protoplasts and are frequently thick-walled and desiccation resistant. When transferred to new medium, brood cells rapidly regenerate new protonemata.

Although protonemal diaspores, and their liberation mechanisms, are most readily observed in axenic cultures, field observation reveal that they are also to be found in nature – often in great abundance (e.g. Orthodontium lineare). Thus protonemal diaspores probably have an important role in the natural reproductive biology of mosses.


Bopp, M., H. Quader, C. Thoni, T. Sawidis & E. Schnepf (1991). Filament disruption in Funaria protonema: formation and disintegration of tmema cells. J.Plant Physiol. 137: 273-284.

Correns, C. (1899). Untersuchungen en uber die Vermehrung der Laubmoose durch Brutorgane and Stecklinge. G. Fisher, Jena.

Duckett, J.G. & R. Ligrone (1992). A survey of diaspore liberation mechanisms and germination patterns in mosses. J.Bryol. 17: 1-20.

Goode, J.A., F. Alfano, A.D. Stead, & J.G. Duckett (1993). The formation of aplastidic abscission (tmema) cell and protonemal disruption in the moss Bryum tenuisetum Limpr. is associated with transverse arrays of microtubules and microfilaments. Protoplasma (in press).

Ligrone, R., J.G. Duckett & A. Egunyomi (1992). Foliar and protonemal gemmae in the tropical moss Calymperes (Calymperaceae): an ultrastructural study. Crypt.Bot 2: 317-329.

Longton, R.E. & R.M. Schuster (1983). Reproductive biology. In Schuster, R.M. (ed.), New Manual of Bryology. Vol. 1, pp 386-462. Hattori Botanical Laboratory, Nichinan.

Prof. M.C.F. Proctor (University of Exeter): Micro-environmental conditions and the growth of Grimmia pulvinata.
Mr D. Long (Royal Botanical Garden, Edinburgh): The hepatic genus Asterella in continental eastern Asia.

Asterella P. Beauv. (syn. Fimbriaria Nees) is one of the largest genera of Marchantiales, in the family Aytoniaceae. From its close relatives Reboulia, Cryptomitrium and Mannia it is distinguished by the unique “pseudoperianth”, a peristome-like structure enclosing the sporophyte. Asterella is of particular interest for its diversity of branching patterns and almost world-wide distribution.

In continental east Asia no fewer than 29 taxa have been described, many of these based on herbarium studies of very inadequate material. Recent field-based studies in the Himalaya and China, combined with a reassessment of character stability, and fruitful study of spore morphology using SEM, have shown that in the past rather plastic thallus characters have been over-utilised and have resulted in great taxonomic confusion and repeated description of some common species under many names. A notable exception has been Kashyap’s work in the north-west Himalaya, based on field studies, with correct understanding of the common species. Kashyap, however, was not able to study types and applied the correct name to only one of his species.

The most useful characters have been branching patterns, sexual condition (paroicous, autoicous and dioicous), morphology of ventral scale appendages and spore colour and ornamentation. SEM studies of spores have been especially useful in placing scrappy type specimens. Eight species are now recognised in continental E. Asia: one dioicous, three paroicous and four autoicous species.

These autoicous species are of particular interest as each has a different arrangement of fertile branching patterns: (1) female terminal on main thallus, male on short ventral branches; (2) male terminal on main thallus, female on short ventral branches; (3) both male and female on short ventral branches and (4) female terminal on short terminal branch and male dorsal on opposite terminal branch which continues as a vegetative innovation.

This last condition is found in an undescribed species recently discovered in the east Himalaya, a feature of which appears to relate it most closely to two or three species in Mexico and California.

The eight species recognised show a diversity of ecology and distribution. Two species are restricted to strictly calcareous substrates, others are more calcifuge. The highest record is from 4,050m in East Nepal. Several species are opportunist and weedy in the Himalaya, especially favouring damp walls, religious buildings such as Buddhist “chortens”, terrace walls and banks on cultivated hillsides. In the Himalaya two species show specialised adaptation to the strict alternation of a wet monsoon season and a dry winter/spring season when xeromorphic thallus branches are produced. Lack of understanding of such seasonal modifications has contributed to past taxonomic confusion.

Dr R.E. Longton (University of Reading) and Yli Yong Min (Guizhou Agricultural College, Peoples Republic of China): Agrobryology in China.

Chinese gallnuts are galls that form on the leaves of sumac trees (Rhus spp.) in response to attack by aphids in the Eriosomatinae. Various mosses from obligate winter hosts for the aphids and thus gallnuts develop only when appropriate species of moss and sumac tree occur in close proximity. The walls of the gallnuts may comprise over 70% tannins and yield compounds of considerable commercial value, notably tannic acid, and gallic acid which derives its name from its occurrence in galls. Gallnuts therefore command a high price, currently around £2.50 per kilogram to the producer, and gallnut production can have a major impact on the local economy in rural areas of China.

At least 14 types of gall have been described from Rhus spp. in China, each caused by a different species of aphid, although the classification of galls and aphids may require clarification. A wide range of mosses act as winter hosts. Of greatest importance commercially is the true-horned gallnut which forms on Rhus chinensis in response to attack by Schlechtendalia chinensis, an aphid that overwinters on members of the Mniaceae, particularly Plagiomnium acutum. There are six generations of S. chinensis in each annual cycle. Reproduction is principally viviparous and parthenogenetic, except for a single sexual generation produced after spring migrants fly from mosses to the sumac trees in April and early May.

True-horned gallnuts are traditionally harvested from semi-natural woodland on rocky hillsides. Approximately 1-2% cover of P. acutum is adequate to support high production of gallnuts provided that it is uniformly distributed, and favourable distribution and abundance of the moss is achieved by transplantation. Attempts are also being made to produce gallnuts by growing sumac trees in agricultural fields, but success is limited by the difficulty of establishing Plagiomnium species in the fields. One solution is to cultivate the moss on soil in plastic bowls which are kept for most of the year in sheds. Five thousand of such bowls are in use at the Tso Ling Zhai Gallnut Experimental Station in Guizhou Province. In October each year the bowls are placed outside under the sumac trees for several weeks and autumn-migrant aphids fly into the moss colonies. The bowls are kept in the sheds during the winter, the moss mat is stripped from the bowls and placed under the sumac trees in April, and spring-migrant aphids then leave the moss and fly to the trees. The moss regenerates in the bowls during summer. We are currently investigating the growth and reproduction of P. acutum as an approach towards increasing gallnut production.

Mr C.C. Townsend (Twickenham): Temperate to tropical – taking the plunge.

There is no reason why any reasonably competent bryologist cannot have a part in advancing the knowledge of tropical bryology; the BBS Tropical Bryology group will help as a vehicle for pooling knowledge and experience. There are four basic near-essentials to begin with:

  1. To have access to, or determination to travel to, a good representative herbarium for checking determinations.
  2. To be prepared to lay out cash for a basic library of books as they become necessary – some expensive (especially Brotherus’ treatment of the mosses in Engler and Prantl’s Die Natürlichen Planzenfamilien ed. 2) , others quite cheap
  3. Be prepared to travel or, often, to recruit those who do (holidaymakers, overseas representatives, missionaries, etc.).
  4. To be willing to seek (but not presume upon) advice of others more experienced.

At the beginning (and these remarks apply to other foreign parts as well as the tropics), set goals:

  1. Is this to be a relaxation alone, to an attempt to contribute to knowledge? A demanding job need not disqualify – Dixon was headmaster of a school for the deaf and dumb.
  2. Am I thinking of one region, or hoping to extend it to the world?
  3. If the world, choose mosses OR liverworts – you can’t do both (though it may be possible for a restricted area)
  4. Shall I name material for expeditions or surveys (a fundamental need), or attempt revisionary work?

Such decisions as these are best made early to avoid gaining knowledge which will be lost later.

It is best to start in a small way, free of pressure of responsibility. Mosses used for packing or brought back by those with no interest in receiving names, or collected personally on a package holiday. Now is a good time to start – there is much more literature on tropical mosses than a few years ago, especially vital checklists; these are invaluable, and even a comparative beginner can produce one by a careful literature survey.

One of the first requirements is to shed preconceptions gained as a result of looking at British bryophytes, such as:

  1. Lots of liverworts have underleaves, but mosses do not (Hypopterygiaceae and Racopilaceae will soon teach otherwise).
  2. It is a waste of time to collect sterile Bryum (e.g. in West Indies much can be done in this state).
  3. Some “key” characters will need a new conception. “Basal cells abruptly demarcated from the upper” is much more extreme in the Calymperaceae than in any European mosses.
  4. Ranges of habitat are found over a comparatively short distance at times in the tropics, with corresponding diversity of bryophytes.
  5. Realising that knowledge of British (even more, European) bryophytes will be of more use than expected in the tropics, both to genera and family, especially in the Old World uplands.

As knowledge of the literature is gained, it will also be realised that many drawings of tropical mosses are excellent. Those of the Bryologia Javanica and Renauld and Cardot’s “Mousses de Madagascar” are every bit as fine as Bryologia Europaea. There are many encouragements for those who will “go for it”.

Mr D. Synnott (National Botanical Gardens, Dublin): The BBS and Irish bryology.

The new Regional Recorder Scheme for bryophytes highlights the continuing difficulty that Irish bryologists have in applying schemes in Ireland which were devised for application in Great Britain. Shortage of fieldworkers both native and imported militates against success of mapping schemes and other network research projects which are extended to Ireland from a base in Great Britain.

Recording of cryptogams in Ireland cannot keep pace with that in Great Britain unless British botanists are prepared to come to Ireland more often than they do at present, both as individuals and in organized groups. The “Troubles” in Northern Ireland have not helped in furthering this necessary process. There was only one member from Great Britain at the recent BBS meeting in Northern Ireland and some really good friends of Irish bryology who have done more than their share of the work in Ireland already were deterred from participating because of their unease with the situation.

Ireland and Great Britain have since the time of Hooker and Taylor been treated as a biogeographical unit for bryophyte recording. The outstanding success of the BBS mapping scheme is a clear indication of the benefits for Irish botany which result from the involvement of British-based botanists and societies.

There have never been more than a few active field bryologists in Ireland. Some of them have made a major contribution to their subject and several species are named for Irish bryologists of the last century, e.g. Templeton, Taylor and Hutchins. It is worth recalling that the forerunner of the BBS, the Moss Exchange Club, was formed following a letter to three journals in 1895, Science Gossip, the Journal of Botany and the Irish Naturalist by a Northern Irish clergyman, Rev. C.H. Waddell of Saintfield, Co. Down. Waddell managed the Exchange until it was on a sound footing and had acquired that momentum which continues to this day.

There may be some British bryologists working in areas already overcrowded with field workers or who would enjoy a change of scenery of habitats. If such a person were to adopt an Irish vice-couinty (there are still thirty-nine to choose from – Limerick has already been adopted) I can give two guarantees, bryological fulfilment and a hearty Cead Mile Failte from the Irish botanical community.

Dr F. Rose (Petersfield) and Mr R.C. Stern (Chichester): Bryophyte distribution in Sussex – the new Sussex atlas.

Sussex (vice-counties 13 and 14) has a bryophyte flora that is remarkably rich for a lowland county in south-east England. Five hundred and fifty one taxa have been recorded, of which 53 have not been seen for many years, and may be extinct; a few others, known until recently, have not been refound in their old localities and may also have gone, but could be found elsewhere.

The richness of Sussex in bryophytes is clearly a result of its varied geology and habitats. The massive sand rocks that outcrop on the sides of several valleys on the Hastings sandstones of the High Weald in East Sussex provide habitats for a number of hepatics and a few mosses that are otherwise absent (or else extremely rare) in England east of Exmoor and south of the central Pennines. The extensive chalk grasslands of the South Downs, particularly on north or east slopes, provide continuing locations for a large number of more exacting calcicole species. The deep gills of the High Weald, with their rocky beds and small waterfalls, have often a bryophyte flora more reminiscent of Wales or the valleys around Dartmoor than of any other areas in lowland England. Finally, there are still considerable areas of wet and dry heath, with occasional valley bogs, on both the Lower Greensand in the west of the county, and on the sands of Ashdown Forest in the east, that provide habitats still present in some other southern counties, but which have largely disappeared from most of midland and eastern England.

A number of slides were shown of maps (mainly tetrad maps from Rose, Stern, Matcham and Coppins, 1991) illustrating the various types of distribution shown by the more local bryophytes of Sussex. In many cases slides were also shown of photographs of the species themselves. These species included a number of the very local Sussex sandrock species (e.g. Harpanthus scutatus, Scapania gracilis, Bazzania trilobata, Dicranum scottianum, Tetrodontium brownianum and Orthodontium gracile) which are still persisting in a number of places. Also included were species of rocky streamsides or flushes in wooded Wealden gills (e.g. Hyocomium armoricum, Hookeria lucens and Trichocolea tomentella) which are still remarkably frequent over wide areas of the High Weald of Sussex and in some cases extend to the wet alder carrs of the Lower Greensand. Local species of humid heaths (e.g. Dicranum spurium) or valley bogs (e.g. Sphagnum papillosum) which still persist in many places on Lower Greensand or in Ashdown Forest; and finally a number of the species of steep, open chalk grassland which are still widespread along the downs, particularly on humid north slopes (e.g. Neckera crispa, Scapania aspera, Frullania tamarisci and Tortella tortuosa), dry south facing slopes (e.g. Pleurochaete squarrosa) or on chalk stones in woodland (e.g. Tortella inflexa). Frullania tamarisci also occurs as an epiphyte on old trees (mostly oaks) in ancient woodland; the question arises, are there distinct ecotypes of this species?


Rose, F., R.C. Stern, H.W. Matcham & B.J. Coppins (1991). Atlas of Sussex Mosses, Liverworts and Lichens. Brighton, Booth Museum of Natural History.

Field excursion to Ashdown Forest, 27 September 1992

The morning was spent in the Duddleswell Valley, high up in the Ashdown Forest. Over 30 members were led by Francis Rose accompanied by the local ranger, Chris Marrabel. An area of wet heath and bog was examined first; 10 Sphagna were seen including S. molle, a rare species in S. England, and confined in Sussex to a few places in the Ashdown Forest. Nardia compressa was seen in reasonable quantity in the stream above the main ravine; in lowland Britain, this liverwort is confined to this site and one further north in the Ashdown Forest. Mark Hill collected Sphagnum auriculatum var.inundatum as well as S. recurvum var. tenue (= S. angustifolium), which was new to Sussex, in boggy parts of the valley, where Jean Paton found Cephaloziella rubella (first recent record for E. Sussex) and C. elachista. In the main ravine, the abundance of Hyocomium armoricum was admired, but Diphyscium foliosum could not be refound. To round off a successful morning, David Long found Cryptothallus mirabilis, only the third record for Sussex, and new to the Ashdown Forest.

The sandrocks at Wakehurst Place were the location for the afternoon excursion. A steadily reducing party saw some of the sandrock liverworts such as Scapania gracilis, Bazzania trilobata and Kurzia sylvatica on the way to Tilgate Wood. The main rocks in the wood were somewhat elusive, mainly as a result of the recent erection of a deer fence, and in searching for these we found the devastation caused by the Great Storm of 16 October, 1987 was still much in evidence. Eventually the rocks were found and a limited number of the party were available to admire Harpanthus scutatus on them.

Rod Stern


Chelwood Gate, Sussex