Fen Management Handbook - Scottish Natural Heritage

The diversity of species-rich tall-herb fens varies across the country with floodplains
in the northwest of the UK dominated by tall sedges, where bottle sedge (Carex
rostrata) is more prominent and uncommon species such as cowbane (Cicuta
virosa), greater water-parsnip (Sium latifolium) and marsh stitchwort (Stellaria
palustris) occur. Upper Lough Erne in Northern Ireland and Insh Marshes in
Scotland provide good examples of these northern floodplain fens.
Seepages and springs on calcareous bedrock provide suitable conditions for a very
different but equally diverse fen flora, characterised by much shorter vegetation
and a greater diversity of low-growing plants, particularly sedges and mosses. In
lowland valley fens fed by low nutrient calcareous groundwater (often from chalk),
black bog-rush (Schoenus nigricans) is often abundant. In the south and east of
the UK this species is restricted to highly calcareous situations, but it also occurs
widely in more acidic conditions in oceanic parts of the country, particularly on
blanket bog in the west of Scotland and Ireland. In amongst the black bog-rush
tussocks a very diverse mix of plants thrive, including small sedges, bog pimpernel
(Anagallis tenella), marsh lousewort (Pedicularis palustris), fen pondweed
(Potamogeton coloratus) and the rare narrow-leaved marsh orchid (Dactylorhiza
traunsteineroides). Many of the remaining sites with this rare fen type are found in
East Anglia, particularly in Norfolk; other important sites are found at Cothill Fen in
Oxfordshire and on Anglesey and the Lleyn peninsula in north Wales.
Tussocks of black bogrush,
with brown mosses
in the runnel. The map
alongside shows the UK
and Ireland distribution of
black bog-rush. (I. Diack)
Black bog-rush map is from the Preston, C.D., Pearman, D.A. & Dines, T.D. (2002)
New Atlas of the British Flora. Oxford University Press.
The northern and upland equivalent of this fen type is usually found around springs
and flushes on carboniferous limestone, and also supports a very distinctive flora,
dominated by small sedges including dioecious sedge (Carex dioica) and flat
sedge (Blysmus compressus). Other characteristic plants include the carnivorous
common butterwort (Pinguicula vulgaris), marsh valerian (Valeriana dioica), and
scarcer species such as bird’s-eye primrose (Primula farinosa) and lesser clubmoss
(Selaginella selaginoides). These generally small fens are particularly characteristic
of the north and west, for example the Craven limestone of Yorkshire and Creag
nam garmin, near Tomintoul, and flushes associated with the basalt rocks of the
Garron Plateau in Northern Ireland.
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