1421 Killarney fern Trichomanes speciosum
Description and ecological characteristics
Killarney fern Trichomanes speciosum is a medium-sized, long-lived fern with delicate, translucent fronds arising from a creeping rhizome. In Great Britain it grows on constantly shaded and permanently humid rock faces, often in deep recesses, in wooded ravines and on cliffs, although in Ireland a wider range of habitats is occupied, and it has colonised numerous old wells in Brittany. The species is frost-sensitive, so that nearly all British localities for sporophyte plants are in mild oceanic districts in the far west and at low altitudes. Most sporophyte populations are very small. However, the gametophyte generation has been recorded from numerous localities (Rumsey et al. 1998), persisting in a state of indefinitely suspended development under present conditions; their occurrence does not alter views on the conservation needs of the sporophytes. The scattered colonies of the mature sporophyte may represent fragmented relics of a wider distribution during warmer post-glacial conditions now surviving under a sub-optimal climate.
The main threat to T. speciosum in the British Isles has been from collecting, but it is also vulnerable to any changes to the flow or chemical composition of the water or to its habitat and microclimate.
European status and distribution
Trichomanes speciosum is confined to Europe and Macaronesia, occurring in Ireland, the UK, western France, Spain, Portugal, north-west Italy, Madeira, the Canary Islands and the Azores.
UK status and distribution
Trichomanes speciosum was always a rare species in the UK, with a scattered mainly Atlantic distribution from Cornwall northwards through Wales and Cumbria to Argyll, and in Northern Ireland. The sporophyte has become extinct at a number of sites due to the activities of collectors and is now very rare in the UK, being known from only a few scattered localities in the north and west. Examples of the gametophyte generation are much more numerous and widespread (Rumsey et al. 1998).
Site selection rationale
One site in northern England and three sites in Wales, all of which also support other Annex I or Annex II features, have been selected to represent this species, but because of the threat from collectors, details of the Welsh sites are withheld. The English site holds the largest known population of Killarney fern in the UK. Only sites supporting sporophyte plants have been considered for site selection. The gametophyte is considerably more widespread, and has been recorded from several sites selected as SACs for other habitat or species features.
Arnecliff and Park Hole Woods
This site contains a greater number of sporophytes than found elsewhere in the UK. However the plants are small, and in many cases not fully developed, with mature spore-producing plants extremely rare. The great significance of this site lies in that the sporophytes appear to be recently developed from gametophytes, a phenomenon that has only been rarely recorded elsewhere in the United Kingdom.
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