Llanelli Naturalists Newsletter - April 2001 - No 5
G S Motley & J J Graham

The area around Bannau Sir Gaer and Llyn Y Fan Fach is well known for the uncommon higher plants, particularly the arctic-alpines, that grow on the Old Red Sandstone cliffs.  These include species such as Northern Bedstraw Galium boreale, Rock Stonecrop Sedum forsteranum, Roseroot Sedum rosea, Dwarf Willow Salix herbacea, Lesser Meadow-rue Thalictrum minus, Cowberry Vaccinium vitis-idaea, endemic Hawkweeds Hieracium spp. and ferns such as Wilson’s Filmy-fern Hymenophyllum wilsonii, Oak Fern Gymnocarpium dryopteris and Beech Fern Phegopteris connectilis.  It is perhaps less well known for its impressive suite of bryophytes more typical of the mountainous areas of North Wales, Northern England and Scotland.    

This account mainly refers to the area bounded by Bannau Sir Gaer (SN801213), the Carmarthenshire/Breconshire boundary and the Nant Melyn (SN809236) and Afon Sawdde (SN802232).   The main habitat types in this area are the cliffs and associated screes, the llyn, rivers and streams, acidic and basic flushes, bog pools, acid heath and acid grassland.  All of the area is common land, which has for many years been subjected to heavy sheep grazing, with the result that most of the vegetation consists of rather species-poor, Mat-grass Nardus stricta -dominated acid grassland.  However, the cliffs are mostly inaccessible to sheep and it is here where most of the interesting bryophytes and vascular plants can be found.  Much of the area has been included in the Mynydd Du Site of Special Scientific Interest, which has been designated for its upland habitat types as well as its geological and geomorphological features, including some of the best British examples of debris flows. 

The earliest bryophyte records from the area result from H.H. Knight’s explorations in Carmarthenshire at the beginning of the 20th century.  The area then appears to have been little explored until the British Bryological Society (BBS) visited the cliffs in 1965, when the liverwort Scapania aequiloba and the moss Schistidium strictum (then known as Grimmia stricta) were amongst the species found.  The BBS revisited the site in 1978 and recorded the mosses Amphidium lapponicum and Gymnostomum calcareum and the liverworts Leiocolea heterocolpos and Moerkia hibernica.   In 1981 the Nature Conservancy Council undertook a survey to establish what plants grew on the cliffs and to learn more about the species assemblages there.  This survey involved abseiling down parts of the cliff and sampling and describing the vegetation on the ledges.  Amongst the bryophytes recorded were the uncommon mosses Grimmia torquata and Oedipodium griffithianum.   Since 1981 the area has been visited by bryologists every few years or so.  Recent new finds include the small liverwort Scapania gymnostomophila (at that time also new to Wales) and the bog moss Sphagnum russowii.

A comprehensive list of bryophytes recorded from the area, together with the recorders’ names and date of the most recent record, is included in Table 1.  An indication of the main habitat for each species is also given.   Nomenclature follows Blockeel and Long, 1998, but synonyms are also listed in Table 1.

Habitats

The grassland and grassland/heath habitats in the area are often tightly grazed and have a rather dull bryophyte flora, generally consisting of conspicuous mats of common pleurocarpous mosses such as Hypnum jutlandicum, Pleurozium schreberi, Rhytidiadelphus squarrosus and Hylocomium splendens.   However, the liverwort Lophozia sudetica, an uncommon species in the county, has been recorded from anthills within some of the grassland stands.  Exposed boulders within these habitats can support interesting moss communities, which vary depending on the base-status of the rock.  Acidic rocks may have mats of Racomitrium heterostichum s.l., abundantly fertile cushions of Ptychomitrium polyphyllum and black patches of Andraea rothii ssp. falcata.   More base-rich rocks often support hoary grey cushions of the mosses Grimmia pulvinata and Schistidium apocarpum s.l.

Bog pools occur scattered across the moorland and there are some small areas of degraded bog, with much bare peat, below the cliffs.  Relatively few species occur here, but the bog moss Sphagnum cuspidatum can be locally abundant and it may cover the surface of pools. 

Flushes and rills occur on steep sloping banks by tracks and streams.   These open, often stony rills, which are best-developed near to the car parking area (SN799238), support relatively few higher plants, with Opposite-leaved Golden-saxifrage Chrysosplenium oppositifolium and Blinks Montia fontana being the main species.  Of the bryophytes found here, particularly conspicuous are the bright yellowish-green patches of the moss Philonotis fontana, swollen reddish-purple mats of the liverwort Scapania undulata and translucent yellow-green tufts of the liverwort Chiloscyphus pallescens.  These rills are also the main locus in the county for Jungermannia exsertifolia ssp. cordifolia, a dark green or almost black coloured liverwort.

The closed flushes are rather variable, with both acidic and base-rich forms present.  The acidic flushes are often dominated by rushes Juncus spp., Polytrichum commune and a variety of bog mosses, with Sphagnum fallax, S. subnitens, S. denticulatum and S. fimbriatum being the most common.   More rarely, S. squarrosum, S. teres and S. russowii are also present.   Where there is some base-enrichment, bog mosses are generally absent, although mounds of S. subnitens are sometimes present on raised areas within the flushes.   Typically these base-rich flushes have an abundance of the yellow-orange coloured moss Palustriella commutata var. commutata.  Other basiphilous mosses which are common in this habitat include Drepanocladus revolvens s.s., Campylium stellatum, Fissidens adianthoides, Philonotis calcarea and Bryum pseudotriquetrum.  The thallose Aneura pinguis, Riccardia chamedryfolia and R. multifida are often the most prominent liverworts.   The mainly coastal liverwort Moerkia hibernica has been recorded from a flush in the area and also from the filter beds on the Sawdde (SN803230), although it has, in the past, been considered introduced, in common with some other mostly coastal species growing here, for example, Variegated Horsetail Equisetum variegatum.  It is quite possible however, that this liverwort is native to the area as it has recently been found at another inland site, Henrhyd Falls near Abercraf, only 12 km to the south-east.  Variegated Horsetail has also recently been recorded seven km to the south-west near Foel Fawr on Mynydd Du and it is typically found in base-rich flushes and beside mountain streams elsewhere in the UK.  Base-rich flushes are generally uncommon in Wales and those in this area may be of some significance in a national context.

Many aquatic or semi-aquatic bryophytes are associated only with the streams and rivers.  The distinctive moss Fontinalis antipyretica can often be found under water, attached to rocks and boulders.  Boulders which are regularly inundated are often covered in one or more of the mosses Brachythecium plumulosum, Hygrohypnum ochraceum, Hyocomium armoricum and Rhychostegium riparium.   Racomitrium species such as R. aciculare and R. aquaticum are also common on stream-side boulders.  Scapania undulata and Chiloscyphus polyanthos are the commonest liverworts associated with this habitat, although Marchantia polymorpha can be locally prominent on rocks, particularly in the Sawdde near the car parking area.  Jungermannia spp. and Pellia spp. may be conspicuous along stream margins.

Footpaths, tracks and walls provide the main locus for the mosses Bryum argenteum, Barbula convoluta, Bryum capillare, Ceratodon purpureus and Tortula muralis.  Eroding banks beside tracks and streams are not without interest and have a typical pioneer community which includes the mosses Pogonatum aloides and Dicranella heteromalla and small liverworts such as Diplophyllum albicans, Nardia scalaris and Jungermannia gracillima.  Less commonly, particularly on eroding stream banks, the mosses Diphyscium foliosum, with its wheat-grain like fruits, and Oligotrichum hercynicum, which resembles a small succulent plant, may be present.

By far the most important habitat for bryophytes are the Old Red Sandstone cliffs below Bannau Sir Gaer (SN797216 to SN819223).   The cliffs are quite variable in that some beds are softer than others, eroding comparatively quickly and producing fine-grained soils, whilst other beds are harder, weathering to form crags and screes.   The base-content of the rocks also varies between beds, creating niches for a mixture of calciphilous and calcifuge species.   The more acidic strata support abundant Diplophyllum albicans, Lophozia ventricosa, Blindia acuta, glaucous patches of Pogonatum urnigerum, black tufts of Andraea rothii ssp. falcata and large dark green cushions of Amphidium mougeotii, whilst the most basic outcrops have large cushions of the mosses Anoectangium aestivum and Tortella tortuosa, both of which are a highly visible bright yellow-green, together with darker patches of Distichium capillaceum and Gymnostomum aeruginosum; also there is often a glaucous-green mat of the liverwort Preissia quadrata in cracks between rocks.  A variety of small liverworts, including the almost filamentous Blepharostoma trichophyllum can be found growing through some moss cushions. 

Species

Several of the bryophytes found on the cliffs are at or very near the southern limit of their range in Britain; these include the mosses Amphidium lapponicum, Encalypta ciliata, Grimmia torquata and Oedipodium griffithianum and the liverworts Leiocolea heterocolpos, Scapania aequiloba and Scapania gymnostomophila.

Scapania gymnostomophila is the only Nationally Rare species (i.e. known from only 1-10 10km squares in Britain) recorded from the area.  Until recently, when it was found in north Wales, this was the only known locality in England and Wales for this liverwort.  It has been found growing as scattered plants over cushions of the moss Anoectangium aestivum and once as an almost pure patch on a cliff ledge.   A total of eight Nationally Scarce species (i.e. known from between 11 and 100 10km squares in Britain) have been recorded from the area.  These are the liverworts Leiocolea heterocolpos, Moerkia hibernica and Scapania aequiloba and the mosses Amphidium lapponicum, Brachydontium trichodes, Encalypta ciliata, Gymnostomum calcareum and Oedipodium griffithianum. 

Most of the species listed in Table 1 have been found or refound since the 1970s and many have been recorded in the last 10 years.  However, two species Marsupella sprucei and Porella cordaeana have not been seen since H.H. Knight recorded them at the beginning of the 20th century.   Bryophytes new to the area have been found almost every time it has been visited and it is likely that other interesting species await discovery, particularly on the mostly inaccessible cliffs.

Acknowledgements

We would like to thank S.D.S. Bosanquet for his comments on an earlier draft of this article.

References

Blockeel, T.L. & Long, D.G.  (1998).  A checklist and census catalogue of British and Irish Bryophytes.  British Bryological Society,  Cardiff.