Meeting report
The original meeting in November having been cancelled because of ravages of Storm Bert, it was with great relief that the weather on the revised date was warm and sunny. This well-recorded valley has a good range of habitats typical of the western Exmoor valleys, but also has some base-enrichment which brings in some more unusual additional communities.
A small but enthusiastic group of six set off along the road from the Robber’s Bridge car park following the course of the Oare Water. The walls in this part of Exmoor have a thick coating of bryophytes and festoons of species, such as Hylocomium splendens, Pleurozium schreberi and Isothecium myosuroides, were soon noted. As we turned off the road to follow a track along the Chalk Water, the more sheltered stone walls were duly inspected and Polytrichastrum alpinum, Scapania compacta and fruiting clumps of Cynodontium bruntonii were identified. In this area, stone walls have increasingly been found to harbour P. alpinum, a scarce plant in the southwest. Sharon spotted a clump of Ptychomitrium polyphyllum which was new to the valley. Interestingly, a patch of Brachytheciastrum velutinum was also found on the wall, this species seems to be declining in this region and crevices in drystone walls appear to be its more favoured habitat here. As we made our way into the valley, we found a good range of river edge and semi-submerged boulder-top species including good populations of Climacium dendroides, Hygrohypnella ochracea, Cinclidotus fontinaloides, Racomitrium aciculare, Hygroamblystegium fluviatile and Chiloscyphus polyanthos, with a nice patch of Hedwigia stellata nearby.
The recent dry weather meant that it was possible to wade right out to the centre of the river and much to everyone’s surprise Sharon came across a cushion of a large Jungermannia growing on a semi-submerged mid-stream rock. Careful inspection indicated that it was J. eucordifolia, with its distinctive heart-shaped leaves. This was subsequently confirmed by Nick Hodgetts as new to south-west England, the nearest known populations being in south Wales. As we got our eye in for the species it was apparent that it was frequent along this stretch of the Chalk Water. Its more usual habitat is flushed upland slopes. After the excitement of finding this liverwort, we tore ourselves away from the river to look at some nearby flushes. Here we found much Scorpidium cossonii, with Campylium stellatum, and Sphagnum such as S. subnitens and S. inundatum, indicating some base enrichment. The predominant moss, however, was the inevitable Calliergonella cuspidata, sporting a bright golden colour and tussocky habit. Sharon climbing a little higher found Pohlia lutescens, another new species for the valley.
We walked on along this most attractive valley and had a welcome lunch break, before tackling some more flushed habitat. The valley opens out along this stretch and a complex of runnels and flushes provided much to search over. Among the ‘brown mosses’, Aulacomnium palustre and Bryum pseudotriquetrum, small patches of Sphagnum contortum and a little S. teres were found. A small patch of the scarce Hamatocaulis vernicosus was found at the edges of a stream. A little further on, we explored a small adjoining valley with steep rocky sides. Here was a new suite of species such as Racomitrium species, including both R. heterostichum and R. obtusum, Orthocaulis floerkei, O. attenuatus, much Lophozia ventricosa and also some of the much scarcer Schistochilopsis (Lophozia) incisa. A series of humid overhangs had cushions of Kurzia trichoclados buried within them. This tiny liverwort, forming dense mats, was initially identified by its strong scent. A small, pale green Scapania with red gemmae on a boulder proved to be S. umbrosa. Previous records in Exmoor for this species have been on rotting wood in the Horner and Barle valley woodlands. A large clump of fruiting Bartramia pomiformis was photographed on the way down to the river edge.
During the walk back we admired a large population of Marchantia polymorpha subsp. polymorpha and copious amounts of a large Fontinalis antipyretica smothering stream-edge rocks. This little stretch of the Chalk Water provided an excellent day out and now has a species list of more than 110 species, including some significant populations, making it a rather special place.
Andrew Branson, 15 April 2025
