We parked at Pont Melin-fach and started off on the west bank downstream of the carpark. This area (SN90611025) holds one of the largest populations of Jamesoniella autumnalis either of us had ever seen, with some Oak trunks supporting 10s of extensive patches.
The entire bryophyte cover on this tree trunk is Jamesoniella!
Remarkably, the Plagiochila punctata trees were in clifftop woodland; Graham is looking at the main tree.
Just before we reached the Plagiochila hotspot, I spotted 6 patches of Drepanolejeunea hamatifolia on a relatively young Ash by a cascading sidestream (SN90871068). This is about 1.5km from the only previous record of Drepanolejeunea from the SAC, found a couple of months ago.
Further upstream, we found an area of rocky woodland where Bazzania trilobata was locally abundant, with 20+ patches in a 10x10m area (SN91001088). Despite Coedydd Nedd a Mellte supporting the best example of Oceanic woodland in south Wales, there are very few colonies of Bazzania on the site, even though this species is found much further south and east in Wales than the SAC's rarer oceanic liverworts.
The final notable liverwort of the day is, like Bazzania, more interesting in a Coedydd Nedd a Mellte context than in a wider south Wales context: we found Colura calyptrifolia on at least 4 Hazel and Ash around SN91121105. Despite this species being found in most of south Wales' conifer plantations, often in great abundance, this is only the 2nd or 3rd time is has been seen in the SAC. It is, of course, a Hyperoceanic liverwort that used to be restricted in Wales to a few of the best oceanic woodland ravines, and its rarity in south Wales' ravines (even where Aphanolejeunea, Drepanolejeunea, Harpalejeunea and Plagiochila exigua are present) is intriguing.
Another section of this amazing site has now been explored, and more bryophyte hotspots found. There's still the area upstream of Pont Rhyd-y-cnau to be done, plus the central Mellte.