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Thelypteris palustris Schott, Marsh Fern

Account Summary

Native, very rare. Circumpolar temperate.

1806; Scott, Prof R.; Scottsborough lakelet.

June to September.

Growth form and preferred habitats

An erect, medium-sized perennial fern with a creeping rhizome from which arise solitary or clumped annual fronds, T. palustris is a decidedly rare species in Fermanagh, confined to the permanently wet, peaty, but not too acidic, muddy ground dominated by sedges, alder and willow around Upper Lough Erne and several of the smaller lakes in the county. Marshes, sedge fens and wet fen-carr woods by small lakes are the typical habitats of the species.

Fermanagh occurrence

As the distribution map indicates, T. palustris is represented in ten tetrads, just eight of which have post-1975 records. It is mainly concentrated in the south of the county, in wet ground around Upper Lough Erne and beside lakes along the SE border of the county. The first Fermanagh record for this species is a recently noted early herbarium specimen in DBN which was collected by Prof Scott from near his home in Scottsborough. Marsh Fern has not been re-found at Scott's site, nor at Hart's pre-1887 station on limestone shingle by the River Erne close to Belleek (a record so vague it probably refers only to the Co Donegal side of the international border (H34)) (Hart 1898), nor at the W end of Inver Lough where it was recorded by Meikle and his co-workers in the period 1946-57.

The sites in the River Finn catchment represent the main concentration of the species in Northern Ireland. The sites in S Fermanagh from which the species has been recorded are: Derrymacrow Lough, Abacon Lough, Farmhill Lough, Clonshannagh Lough, Lough Garrow, Killynubber Lough, Inver Lough, the lakelet by the avenue at Crom and the River Finn near Gortnacarrow Bridge. T. palustris is even rarer in adjacent Co Cavan (H30), where only one of four stations has a recent (1996) record (Reilly 2001). Similarly in Co Tyrone (H36), which had two late-19th century sites for the fern, it only persists at Enagh Lough, near Caledon (McNeill 2010).

Page (1997) regards Marsh Fern as a plant of essentially Continental climatic conditions. Since Fermanagh is decidedly oceanic (or Atlantic) in its climate, and the local T. palustris sites lie within 12-25 km of the west coast of Ireland, the species must be close to the extreme margin of its range, where it is often and extensively replaced by Osmunda regalis (Royal Fern).

Irish and British occurrence

Throughout both Ireland and Britain, T. palustris is a scarce and widely scattered species. The Census Catalogue of the Flora of Ireland lists past records from a total of 21 VCs, but the map in the 1978 Fern Atlas records only 14 Irish hectads with post-1930 records (Jermy et al. 1978), while the New Atlas map plots 18 hectads with post-1987 records (Preston et al. 2002).

In Britain, while slight concentrations occur on the Isle of Wight (VC 10) and S Hampshire (VC 11) (Brewis et al. 1996), and again in Norfolk (VCs 27 & 28) (Beckett et al. 1999), Marsh Fern becomes much rarer north of a line between Hull and Liverpool (Jermy et al. 1978; Stewart et al. 1994; Preston et al. 2002).

European and world occurrence

Marsh Fern ranges widely across warm-temperate latitudes of mainland Europe stretching east to Siberia. In the north it reaches N Finland, and it stretches southward to the southern tip of the Peloponnese in Greece, the distribution thinning markedly in both directions (Jalas & Suominen 1972, Map 73). Taking the species in the broadest taxonomic sense, it is disjunctly circumpolar, with gaps in N Asia and in the eastern half of N America. The NE American and E Asia forms of the plant are now sometimes recognised as varieties of a separate species, T. thelypteroides (Michaux) Holub. A form of T. palustris s.l. is also found in S Africa, S India and New Zealand, now referred to T. confluens (Thunb.) Morton (Hultén 1962, Map 170), or to T. palustris subsp. squamigera (Schlecht) Hult. (Hultén & Fries 1986, Map 38; Page 1997). Without the insight of a trained taxonomist, I am amazed and a little disconcerted by the fact that Thelypteris palustris has been referred in the past to as many as six other genera, some nowadays totally unfamiliar, so that index searching in older texts often works much better using the more stable English common name (Hultén 1962).

Names

The genus name 'Thelypteris' is a Greek compound meaning 'Lady-fern', a name first used by the ancient Greek botanist, Theophrastus, for an unspecified fern. The specific epithet 'palustris' is Latin (given a masculine ending), and means 'of swampy places' (Gilbert-Carter 1964). The standard English common name of T. palustris is nowadays 'Marsh Fern', a folk name suggested by its habitat. Previously it was also called 'Marsh Buckler-fern' and, in the Isle of Wight, 'Ground Fern' (Step & Jackson 1945).

Threats

In Fermanagh, as elsewhere in Britain and Ireland, agricultural drainage, cultural eutrophication and scrub encroachment is making inroads on suitable habitats, and Marsh Fern is becoming increasingly rare (Hackney et al. 1992).