Trichomanes speciosum – killarney fern
Trichomanes speciosum Willd.
Family: Hymenophyllaceae
Named after Killarney in SW Ireland where it was once abundant, but is now greatly diminished because of collecting. In Northern Ireland the sporophyte is an extremely rare plant with just one extant site, but the sexual stage (gametophyte) is locally frequent in County Fermanagh.
In brief
- A fern, with two very different stages or generations, one sexual (gametophyte) and one spore-producing (sporophyte)
- Both generations inhabit damp caves or rock clefts
- Sporophyte currently known from one site only in Northern Ireland
- Gametophyte known from the Lough Navar Forest at several sites
- Listed as a UK Priority Species
- Sporophyte population very small and vulnerable to total loss.
Species description
Sporophyte: a small fern with a creeping rhizome from which rise the leaves. Each leaf is translucent and dark green in colour, up to about 20cm long; much divided into narrow segments so that the whole leaf is ‘feathery’ in appearance. The leaf stalk is about the same length as the leaf blade itself. Spores are produced on small bristle-like projections at the ends of some of the leaf segments.
Gametophyte: totally unlike the sporophyte and resembling a greenish felt on the surface of the rock on which it grows. It consists of a mesh of fine thread-like filaments among which are produced the male and female sex organs.
Life cycle
Like almost all ferns, Killarney fern exhibits alternation of generations in which the spores germinate to produce the gametophyte stage which in turn produces male and female sex organs. The female organ contains an egg, which, when fertilised, develops into the mature sporophyte plant. However, it has been observed that the gametophyte can persist for years without producing any sporophytes and in parts of the range of the species, sites for the gametophyte far outnumber sites for the sporophyte.
Similar species
There are no similar species with which this fern could be easily confused.
How to see this species
Because the sporophyte is confined to a single site (and probably a single plant) it is not practicable for it to be visited without special arrangement.
The gametophyte is readily accessible in a number of caves in the Lough Navar Forest, County Fermanagh, such as those beside the path alongside Lough Achork. These sites are very dark and best examined with the aid of a flashlight. Relevant access permissions should always be sought prior to visiting any sites.
Current status
The sporophyte seems to survive only as a single individual plant in a shallow cave near the seashore in County Antrim. A nineteenth century site in Strabane Glen, County Tyrone has disappeared.
The gametophyte is locally abundant in the Correl Glen – Lough Navar Forest area of County Fermanagh. The map in the new BSBI Atlas 2002 (Preston et al.) is inaccurate and omits these sites.
Why is this species a priority in Northern Ireland?
- Listed as a UK Priority Species.
It is listed in the Irish Red Data Book as rare.
Threats/Causes of decline
In Northern Ireland this has never been an abundant species since recording of the flora began. In Ireland and Great Britain generally, over-collecting by gardeners and botanists in the Victorian era caused massive decline.
The principal threats in Northern Ireland appear to be that the sporophyte population is unviable and dangerously tiny, while the gametophyte population appears stable and unthreatened. The failure of the gametophytes to produce sporophytes is another factor in the continued rarity of the species and its failure to spread beyond existing sites.
Conservation of this species
Current action
There is a UK Species Action Plan which was published in 1995.
- One gametophyte site is situated in a National Nature Reserve (Correl Glen)
- Several sites are contained within Lough Navar Forest, maintained by the Forest Service
- The lost nineteenth century site in Strabane Glen is within an Ulster Wildlife Trust Reserve
- Implementation of the Northern Ireland habitat action plan for Oakwoods.
Proposed objectives/actions
- Maintain existing sporophyte population
- Seek to ensure the requirements of the species are taken into account in site management plans and attempt to secure favourable management agreements for sites containing this species which are not protected through designation
- Ensure that landowners are aware of the importance and legal status of this species, appropriate methods of habitat management for its conservation and the threats currently facing known populations
- Compile an inventory of all sporophyte populations in cultivation, in botanic gardens and private collections, and establish provenances if possible
- Monitor County Antrim sporophyte site on a regular basis
- Relocate the ‘lost’ Strabane Glen site.
What you can do
Records of the sites where you see this species are important, especially of the sporophyte. Send any records to either BSBI, c/o Department of Botany, National Museums Northern Ireland, 153 Bangor Road, Cultra, Co. Down, BT18 0EU or to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Co. Down, BT18 0EU Tel: 028 9039 5256, cedar.info [at] nmni.com.
Further information
Northern Ireland Habitat Action Plans
Literature
Curtis, T.G.F. and McGough, H.N. (1988). The Irish Red Data Book – 1 Vascular Plants. Stationery Office, Dublin.
Hackney, P. (1992). Stewart & Corry’s Flora of the North-east of Ireland, 3rd Edition. Institute of Irish Studies, Belfast.
Preston, C.D., Pearman, D.A. and Dines, T.D. (2002). New Atlas of the British & Irish Flora. Oxford University Press/DEFRA.
Text written by:
Paul Hackney
iNaturalist: Species account : iNaturalist World Species Observations database