Until the 1990s, British Hedwigia were pretty easy to identify: if they had hairpoints they were H. ciliata and if hairpoints were absent they were H. integrifolia. Lars Hedenas revised the genus in northern Europe in 1994, leaving Britain with four taxa: the common one turned out to be H. stellata (below left), the much rarer H. ciliata had two varieties here, and H. integrifolia stayed the same (but subsequently changed genus to Hedwigidium). Roll on to 2010, and Portuguese researchers published good evidence that there is an additional species in western Europe: Hedwigia striata (below right). This has turned out to be relatively widespread in Portugal, but intriguingly it was described new to science by Warrington bryologist William Wilson with an 1829 Type Specimen from Llyn Idwal in north Wales.
Hedwigia striata was an obvious target for last week's British Bryological Society meeting in Eryri (see #EryriMosses on Twitter for other finds made during the week). We marched past Llyn Idwal on our way to Llyn y Cwn and didn't see any Hedwigia, but a search of lakeside boulders along the lake's north shore in 2013 had failed to reveal anything other than the common H. stellata anyway (a search of the south shore could be worthwhile). Groups also checked for Hedwigia at Llyn Bochllwyd and Llyn y Cwn in the Glyderau, and at Ffynnon Llyffant and Llyn Crafnant in the Carneddau, but the only place with anything different was Ffynnon Lloer (below) in the SW Carneddau.
Ray Woods had collected Hedwigia "ciliata sensu stricto" from there a few years ago, before H. striata had been resurrected, so we had high hopes that this natural, un-dammed lake might have good rocks. Sure enough, Barry Stewart found a short-pointed Hedwigia on the first rock we checked, and subsequent searching on the south shore produced at least 3 more colonies along with Bryum muehlenbeckii, whilst a 4th was found growing alongside Pterigynandrum filiforme on a rock on the north shore. We assumed this was Ray's H. ciliata, but I started to get excited when I noticed that all of the dry leaves had very obvious striations/pliccations along their length. All four colonies we found showed this feature, and subsequent microscope checking confirmed that this really was H. striata, rediscovered in Eryri 196 years after the last record and on a new lake (it may well have gone from Llyn Idwal because that lake has been modified somewhat by a dam). An additional feature mentioned in Flora Briofitica Iberica is the presence of long papillae on the basal leaf margin, and the Ffynnon Lloer plant shows these even more prominently than the FBI illustrations!
My next task is to revisit other British specimens of Hedwigia ciliata from upland lakes and other habitats, particularly some I collected from Llyn Gafr on Cadair Idris a couple of years ago (specimen in BBSUK). This is an outstandingly interesting habitat with plenty of rare and scarce species, but one that has been rather under-valued bryologically in Wales. In recent years bryologists have recorded the following by Welsh mountain lakes: Bryum muehlenbeckii (Nationally Scarce), Grimmia anomala (Nationally Rare), Grimmia muehlenbeckii/austrofunalis (Nationally Scarce, please don't flame me for sitting on the fence with taxonomy), Grimmia ramondii, Odontoschisma elongatum (Nationally Scarce), Orthotrichum rupestre, Pterigynandrum filiforme (Nationally Scarce), Racomitrium macounii (Nationally Scarce), Schistidium agassizii (Nationally Scarce) and probable Schistidium trichodon (Nationally Scarce). Interestingly, most of these have only been found on un-dammed, natural lakes and most are present on fewer than 5 rocks on any lake.
I know this blog is called "South Wales Bryophytes" and this moss is in North Wales but two regular contributors (Barry and me) were involved in the search! Barry has some much better photos of the leaf striations, which I hope he might add to this posting. [The dry and wet images added below are the best I have demonstrating the plicate leaves - BS]
[Two more photos of the small sample I brought home provide better resolution - BS]