Spent a very windy, sand-blasted morning with Barry and Becky Sharp (NPT Wildlife Team) looking at Margam Tip, a very biodiverse site and a fascinating example of sand dune remediation. During a whistle-stop tour of the open mosaic perimeter of the steelworks, we stopped to look at a wet sandy area with Ranunculus trichophyllus, Juncus ranarius (= J. ambiguus) and Plantago coronopus, typical species of damp, brackish sand. I just happened to say 'this looks like a good place for Riccia cavernosa' before Barry exclaimed 'yes, and here it is'. There were approximately 500 individuals in an area of about 100 square meters.
Unfortunately this particular site will undergo development which will almost certainly result in the loss of this population. However, we are hopeful that habitat creation elsewhere will provide suitable habitat for it; i.e. wet, base-rich, sandy mud which is subject to winter flooding. Some inoculation may help. The occurrence of associates like R. trichophyllus, J. ranarius and P. coronopus seems to indicate the suitability of these habitats for this exquisite liverwort. There's something quite special about Crystalworts.