Thelypteris palustris

Taxonomy 

The current name is Thelypteris palustris Schott, Marsh Fern, and it is the only member of that genus in Britain. However, its taxonomy has been revised many times in the past so it has a lot of synonyms which are now rarely used but which feature on voucher specimens and in literature, especially from Victorian times. Here are some of the more commonly encountered ones.

Synonyms (all obsolete):

  • Acrostichum thelypteris L.
  • Aspidium thelypteris (L.) Sw.
  • Dryopteris thelypteris (L.) A. Gray
  • Lastraea thelypteris (L.) Bory
  • Nephrodium thelypteris (L.) Strempel
  • Polypodium palustre Salisb.
  • Thelypteris thelypteroides Michx.

The name ‘thelypteris’ (thele + pteris in Greek) is usually considered to mean ‘female fern’ although it could just as easily be ‘nipple fern’. Neither is very helpful.

Chromosome no.: 2n = 70 (Stace 2010).

Thelypteris palustris

Photography: A.J.Lockton

Distribution 

Throughout Britain and Ireland as far north as central Scotland. Throughout the northern temperate zone in Europe, Asia and North America. Scattered occurrences elsewhere. Populations in eastern Asia and North America are sometimes considered to be of a separate subspecies to British plants (Page 1997).

Thelypteris palustris

Photography: A.J. Lockton

BSBI Hectad Map 

Click on the map to view full-size on the BSBI Maps Scheme website.

Ecology 

Accounts by various authors differ about whether or not it is restricted to a peat substrate. Page (1997) describes it growing ‘where deep silty mud becomes trapped.’ But more often it is said to be restricted to base-rich peat in places such as the Norfolk Broads, where it is still common. Rodwell (1991) recorded it in three vegetation communities: M22 Juncus subnodulosus fen-meadow, W2 Salix cinerea woodland and W5 Alnus glutinosa woodland. It is found in both open sunlight and in light woodland. It also occurs in W4 Betula pubescens woods, which form when Sphagnum mires receive an influx of surface water and begin to succeed to woodland. It is a lowland plant. In 1891 it was recorded at c.335 m at Braemar (Pearman & Corner 2009), but it has now gone from there. The current highest population is unknown.

Status 
  • Origin: native throughout Britain and Ireland.
  • Rarity: Nationally Scarce in Britain (Stewart et al. 1994). If there was an equivalent status in Ireland, it would probably qualify for it. In Scotland, however, it is very rare.
  • Threat: there has been a considerable decline throughout its range, especially in eastern England and Scotland. The cause is probably habitat loss due to drainage.
  • Conservation: an axiophyte in any county in which it occurs.
  • Legislation: no specific legal protection.
Further Work 

This species is rare enough that its sites warrant fairly frequent monitoring (every ten years) to provide early warning of further losses. All its sites should probably be SSSIs, as it is indicative of habitats that are now very rare and threatened in the British Isles. A full audit of sites would therefore be worthwhile. A shortage of information on its habitat and vegetation communities is apparent. It seems to occur in either the transitional vegetation at the edges of mires, or in habitats of intermediate successional stages. If the latter, then it would need to be able to colonise new sites quite readily (which is easy to envisage for a fern), but is there any evidence of such colonisation in the data?

References 
  • Page, C.N. 1997. The Ferns of Britain and Ireland, 2nd edition. Cambridge University Press, Cambridge.
  • Pearman, D.A. & Corner, R.W.M. 2009. BSBI projects: Altitudinal Limits.
Citation 
Lockton, A.J. (date accessed). Species account: Thelypteris palustris. Botanical Society of the British Isles, www.bsbi.org.uk.

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