Hymenophyllum tunbrigense Tunbridge Filmy-fern

Hymenophyllum tunbrigense, Tunbridge Filmy-fern, is a small, dark green, rather moss-like fern with delicate, almost transparent, flattened fronds which form mat-like masses on vertical rock faces or tree trunks in humid, shaded places. It is quite intolerant of desiccation. It is an Atlantic species which is rather scarce in Britain overall and mostly a plant of ravines and stream valleys in north-west Scotland, south-west Ireland and some parts of Wales, particularly north-west Wales. It is a notable feature of the waterfall country in the headstreams of the upper Neath Valley in the Brecon Beacons National Park (Bannau Brecheiniog), but there are only 2 known (extant) populations of Tunbridge Filmy-fern in west Glamorgan which occur in the Melincwrt Valley and Cwm-du Falls. It can be confused with Wilson's Filmy-fern (Hymenophyllum wlsonii), a more common species nationwide, and it is best distinguished from it by the structure of the sporangia whose outer edges are flattened and coursley toothed - those of Wilson's Filmy-fern have a smooth outline. Tunbridge Filmy-fern is much less common than Wilson's Filmy-fern in Britain.

Native