264 THE WILTSHIRE ARCHAEOLOGICAL AND NATURAL HISTORY MAGAZINE 
D. praetermissa (and its hybrids with D. fuchsi) and 
Small Nettle Urtica urens. Greater Pond-sedge 
C. riparia 1s rather more common here. The Water 
Dock Rumex hydrolapathum is a prominent feature 
along the streams. There is a very small colony — in 
some years only one spike — of Green-flowered 
Helleborine Epipactis phyllanthes, which is rare not 
only in Wiltshire — found in only eight 1 x 1 
kilometre squares — but also nationally. 
Green-flowered Helleborine 
Within this tall fen there is about a quarter of a 
hectare where the peat is floating. Part of it has a 
short turf and, unusually for the reserve, a lot of 
moss. This kind of mire is typical of spongy peat 
moistened by calcareous, base-rich waters. Here are 
large numbers of Bogbean, M. trifoliata and of 
Marsh Arrow-grass Triglochin palustre. This latter 
species was found in only nineteen kilometre 
squares by the Wiltshire Flora Mapping Project. At 
one time it was struggling on the reserve under 
competition from grasses and sedges. Grazing at 
this colony, and close cutting and light trampling 
during the winter (inadvertent but, as it turned out, 
beneficial) in the compartment mentioned next, 
have restored its fortunes and now, in 2003, there 
are hundreds of spikes. 
Bogbean 
Adjacent to the grazed fen, but fenced off from 
it, is another Carex-dominated mire covering about 
three quarters of a hectare [6]. It would be difficult 
to manage cattle on it, so it is not grazed but cut and 
raked every winter. (The raked heaps form excellent 
breeding grounds for the Grass Snakes Natrix natrix 
which are a feature of the reserve.) Not only does 
this small enclosure have the richest flora of the 
reserve with several Wiltshire rarities, but there are 
within it fascinating juxtapositions of plants 
characteristic of acid and of alkaline soils. 
As an indication of its richness, of the 81 species 
of vascular plants listed for the south-west fen, 31 
are found only here. It also has many species of 
moss, including a small patch of Sphagnum palustre. 
Bogbean sward in South-west Fen 
