Yes, I know all tetrads are the same size, but in terms of land area ST16C must be one of, if not the, smallest in the county. It contains the very tip of Friars Point at Barry Island - probably no more than 300 square metres of dry land above the inter-tidal.
I was down on the beach at Barry Island with the family yesterday so decided to take a quick look, given the lack of any previous records. Irritatingly I'd forgotten my phone/GPS so wasn't sure exactly where this tetrad started, and so took a cautious approach and only looked for bryos right at the point. Looking at the map when I got home, there was a bit more land in ST16C than I realised - so I'll have to have another look next time I'm there.
The samples I grabbed comprised only two species, both from thin soil among the limestone rocks: Tortella flavovirens and a Tortula (I think) which has me puzzled. Photos below.
Initially I thought this was T. modica but the cells are at least moderately papillose, the margins aren't obviously recurved and the leaf tip is a bit toothed. The latter character made me think it might be Hennediella but I think the seta is too short (only about 4mm). It doesn't seem to fit any of the other Tortula species very well. Any suggestions?