Trichomanes speciosum Willd., Killarney Fern

Account Summary

Fermanagh occurrence

The discovery of this very distinctive fern in Fermanagh was announced in the Irish Naturalist of December 1900 when R.Ll. Praeger wrote, "The investigations of Messrs. West and Tetley have added the Killarney Fern to the Flora of Co Fermanagh. They sent me a specimen last August, describing the exact locality – a deep crevice in limestone rocks; but I think it better not to publish the station, so terribly has this lovely plant suffered from the depredations of unscrupulous collectors." The following year Praeger included mention of the station in his monumental Irish Topographical Botany simply as, "Near Carrick". The site was more clearly identified as the Correl Glen in the unpublished Typescript Flora of Co Fermanagh of 1951. The rocks in the area around the Correl Glen are limestone and calcified or dolomitised sandstone. The glen supports old, moist, mixed deciduous woodland, growing on peaty soils at an altitude of around 100 m.

Growth form and preferred habitat

Killarney Fern is closely related to the genus Hymenophyllum and is another type of filmy-fern having rather larger, dark-green, membranous, translucent fronds, 7-60 cm in length and much divided (Ratcliffe et al. 1993). Unlike both of the Hymenophyllum species, however, T. speciosum typically resides near waterfalls or mountain streams in sheltered, deep, shady rocky gorges, growing in rock crevices between boulders, in dripping caves or under overhangs where spray or seepage water keeps the plant permanently moist and dripping (Page 1997). Almost all of its British & Irish stations past and present have been in mild oceanic districts in the far west and often at low altitudes. Evidently it is a warmth-demanding species requiring a great deal of shelter, and probably it is rather frost sensitive, a feature which contrasts strongly with the much more hardy Hymenophyllum species (Wigginton 1999).

Gametophyte generation

The prostrate, sexual, gamete-bearing gametophyte generation of Trichomanes was first recognised by Mettenius in cultivation as long ago as 1864. Uniquely amongst European ferns, the gametophyte reproduces vegetatively in the absence of the asexual spore-bearing generation, the ± upright, or else dangling, frond-producing sporophyte. The independent gametophyte populations were completely overlooked in Britain until 1989 (Rumsey et al. 1992).

In February 1993, Nick Stewart visited Fermanagh with an international group of bryologists. When examining mosses and liverworts in the Correl Glen and on the overhanging scarps of Lough Navar Forest Park, he twice found the gametophyte of the Killarney Fern. RHN was on the outing and learnt how to identify this green, thread-like sexual stage of the fern life-cycle. Since 1993 he and his wife Hannah have found it in twelve tetrads spread across three hexads. Many of these gametophyte finds have been verified by staff at the Natural History Museum, London. The southerly, most isolated site shown on the map is in a deep, dark hole in a scarp at Aghnahoo, on the slopes of Cuilcagh mountain.

The gametophyte grows in Fermanagh under deep, dark rock overhangs, usually about an arm's length removed from the light. It is the last form of plant life to grow before light levels become totally inadequate. The gametophyte forms patches which vary in size from several square centimetres to almost the size of one's hand in exceptional cases. It is light green, looks like a filamentous alga, and has a spongy texture when pressed down. When viewed under a hand lens it looks like wire wool with small spikes sticking out from it like the thorns on certain rose bushes. The inability of all these gametophyte plants around the British Isles to carry out successful sexual reproduction and develop new mature sporophyte frond-bearing plants, means that the high conservation status of T. speciosum, ranking it as vulnerable, must remain in force. Along with other oceanic species, Killarney Fern is considered by some conservation biologists to be at further risk from the predicted effects of global warming (Plantlife 1991).

Further detailed study of the exact growth requirements of T. speciosum is urgently needed, and an investigation as to why the gametophyte fails to produce new sporophyte plants would also assist conservation and rehabilitation efforts associated with increasing biodiversity awareness.

Robert Northridge rediscovers the sporophyte

On 1 May 2005, while searching for the gametophyte under a large rock at a location within the H05 hectad, RHN discovered a solitary plant of the sporophyte. It consisted of two fronds each 8 cm long, one frond 6 cm long, another frond 6 cm long but with the top half dead, plus the broken stipe only of another frond. There was also a small patch of the gametophyte about 15 cm × 10 cm close by. When the sporophyte site was visited a year later on 26 May 2006, as well as the previously seen fronds, there was a new frond unfurling which was just over 5 cm long.

This site was in a very sheltered, cave-like area under large fallen rocks through which there is no perceptible flow of air that might dry and damage the wet filmy fronds. The site is under trees and the entrance to the 'cave' is overhung by dense straggling leaves of Luzula sylvatica (Great Wood-rush). Exact details of the location of this site have been lodged with the Northern Ireland Environment Agency (NIEA) in Belfast.

The rediscovery of the Fermanagh Trichomanes sporophyte has been the recording highlight of this whole VC Flora project.

Gametophyte Irish occurrence

The Trichomanes gametophyte has been recognised in numerous Irish sites and by 1998 was known from 13 VCs. In Britain, the same published report listed the gametophyte from a total of 38 VCs and provided a map for both islands (Rumsey et al. 1998, Figure 4). Since then isolated finds of the gametophyte have been made in Cos Tyrone and Antrim (H36 and H39) and we are confident that this generation of the species remains under-recorded.

Previous Irish occurrence of the sporophyte

In the early 19th century, the sporophyte of T. speciosum was found to be frequent and widespread in and around Killarney and SW Ireland in general (Jermy et al. 1978; Wigginton 1999). On account of the beauty and comparative rarity of the fern, T. speciosum became the supreme target of collectors and gardeners during the long-running Victorian Fern Craze (1830-1920) (Allen 1969; Page 1988).

The Victorian Fern Craze in SW Ireland

Kerry and other parts of the west of Ireland attracted many visitors on account of its wealth of fern species, and since T. speciosum appeared in such abundance in the region, it probably seemed harmless to remove a little of it in order to grow the lovely fern in one's front room in a glazed Wardian Case or in a Conservatory, or to press and dry it for the family herbarium collection. Visitors found the fern easily, and there was no difficulty in pulling it down from its wet rock under-hang or cave roof habitat. In fact, the long strands of bristly, black, rhizome came away far too readily, and it is very likely that visitors accidentally removed far more of the plant than they ever wanted to transport. At one stage, tinkers collected Killarney Fern and hawked boxes of it around the Killarney hotels, selling it to visitors, until eventually the extremely slow-growing plant was reduced to extreme rarity and local extinction (Marren 1999).

A lingering collective cultural guilt is the reason why naturalists are now so extremely circumspect about the remaining stations of the Killarney Fern in the British Isles, and it is now recognised as a Red Data Book species, protected by conservation laws in both Britain and Ireland.

Irish occurrence

In Ireland, over the years, the sporophyte T. speciosum has been recorded from a total of 43 scattered sites. The Irish Red Data Book (1988) reported that it had been recently found in just ten of these sites. A subsequent study of T. speciosum habitats in the British Isles made by Ratcliffe and his associates found the sporophyte was still quite widespread in the hill country of Cos Kerry and Cork, where they located a total of 26 'colonies' (ie individual patches, each representing a single rhizome system). These workers reckoned they had searched only a small part of the total possible ground in SW Ireland that might support the sporophyte generation. Nevertheless, they concluded that T. speciosum is a much reduced species, and that some of the more outlying Irish colonies were also collected out of existence besides the ones previously known about in Cos Kerry and Cork (Ratcliffe et al. 1993).

Similar depredations befell the much more thinly scattered populations in England, Scotland and Wales, where sporophyte T. speciosum is now confined to very few localities. Ratcliffe and his associates located a total of just 13 of their individual 'colonies' in Great Britain, details of which are kept so secret that their map references do not even appear on the confidential computer records at the Biological Records Centre at Monkswood (Ratcliffe et al. 1993; Marren 1999).

Field observations suggest that under existing environmental conditions Killarney Fern has been incapable of producing any new sporophyte populations for over a hundred years. Again, like other filmy-ferns, growth of the fern is very slow. Each frond can continue growing for five or more seasons, and individual colonies that have been observed and measured over many years, do not appear to change in appearance or show any significant growth (Ratcliffe et al. 1993).

World occurrence

Reflecting the climatic limitations discussed above, T. speciosum is confined to a very limited mild, damp oceanic area of Europe and the Atlantic isles (Azores, Madeira and the Canaries). Besides the British Isles, it occurs only in Brittany, the Pyrenees, near Gibraltar and near the west coast of N Italy in the Alpi Apuane at between 180-250 m (Jalas & Suominen 1972, Map 71; Ratcliffe et al. 1993; Pignatti 1997, vol. 1, p. 53; Rumsey et al. 1998).

Uses

There does not appear to be any folklore about the fern, nor is it credited with any medicinal properties. It has, of course, been valued for its showy beauty and rarity and has been cultivated by keen gardeners since its discovery. Trichomanes is a cosmopolitan genus and contains a total of 25 species, most of them tropical, and the majority in horticulture originate from the southern hemisphere (Griffiths 1994).

Names

The genus name 'Trichomanes' was given to an unknown fern species by Theophrastus (possibly Asplenium trichomanes, Maidenhair Spleenwort). Gilbert-Carter (1964) regards its origin as obscure, but it is definitely a Greek compound involving 'thrix, thichos', meaning 'a hair', 'a bristle', or 'hairy' (Stearn 1992). One idea for the derivation of the other half of the genus name is the Greek 'manos', meaning 'flexible', but there is some doubt as to the relevance of this suggestion, and the correct derivation therefore remains a mystery (Step & Jackson 1945).

The specific epithet 'speciosus' is Latin meaning 'showy' or 'handsome'.

Threats

All the currently known sites are within ASSIs. Further study of the ecology and biology of the species is urgently required in order to properly manage its conservation.

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