A quick follow-up from my visit to Coed Tremadog last Friday. I collected some Radula from a large patch on a basic igneous rock in south-facing coastal woodland in the hope it might be R. lindenbergiana. There was also R. complanata on rocks in the wood, but all was abundantly fertile (monoicous with male bracts below perianths, and often with fruit) whereas this large patch appeared sterile in the field. A microscope check revealed the collected Radula to be dioicous female R. lindenbergiana, with pairs of long-keeled, large-lobuled female bracts. The female bracts in the photo are especially distinctive, sitting between a pair of branches.
The only south Wales record of Radula lindenbergiana comes from south-facing rocks in central Pembrokeshire, but apparently non-fertile Radula has been found a couple of times in southern coastal areas and the species' distribution in SW England suggests we may be overlooking it. Confirming dioicous colonies is not easy though!