I noticed several small rocks covered in Heterocladium during a family walk at Coed-y-wenallt (North Cardiff ridgeway) yesterday. This came as a surprise as the wood is generally of little bryological interest and lacks humidity-demanding species, though I haven't had a proper look at Nant Cwmnofydd in the valley bottom (though Peter Sturgess and Roy Perry have recorded here).
Yesterday's sample proved to be H. heteropterum var. flaccidum, which updates an old Atlas record for ST18 made at the same site by A.E. Wade in 1951. The colony I found was by a footpath at ST149830 and could conceivably be the same colony that Wade recorded 65 years ago.