The scree below the outcrop is populated with large amounts of Racomitrium lanuginosum, R. fasciculare and Stereocaulon vesuvianum but there are some nice patches of Huperzia selago here too. Much of the Andreaea on the slabs is A. rothii ssp falcata, but there is also a small amount of A. rupestris.
Huperzia selago and Stereocaulon vesuvianum
Also of interest below the main outcrop is the frequent occurrence of Barbilophozia floerkii and lots of Lophozia ventricosa. We searched for L. sudetica but failed to find any convincing material.
With optimism we climbed up to the outcrop, but the best we could find was a small patch of Hymenophyllum wilsonii, which is frequently present on north-facing sandstone in RCT (and never disappoints). Other stuff included Heterocladium heteropterum, Pohlia nutans and Racomitrium aquaticum. All in all it is a typical, if not spectacular, collection of upland species on a relatively small outcrop which is quite near to a very busy road. You might expect Oreoweisia bruntonii and Bartramia here too, but if they are there they escaped us.
Tony Smith (in A Bryophyte Flora of Glamorgan) describes the Rhondda sandstone outcrops as mostly east-facing and relatively species-poor. I don't know to what extent that has deterred people from exploring these cliffs, but it might explain why species like B. floerkii have been regarded as rare in Glamorgan. In my experience even the small outcrops are worth a look.