Bogbean  (Menyanthes trifoliata)

Dune slacks: depressions between sand dunes that are often wet during the winter.
Perennial: plants that live for at least three seasons; after an initial period they produce flowers once a year
Rhizomes: rhizomes are thickened, branching, creeping storage stems. Although most rhizomes grow laterally just along or slightly below the soil's surface, some grow several inches deep. Roots grow from the underside of the rhizome, and during the growing season new growth sprouts from buds along the top. A familiar rhizome is the ginger used in cooking.

1. National Biodiversity Network Species Dictionary (September 2003):
   http://www.nhm.ac.uk/nbn
   
2. Clapham, A.R., Tutin, T.G., and Moore, D.M. (1987) Flora of the British Isles 3rd Edition. Cambridge University Press, Cambridge.
   
3. Preston, C.D., Pearman, D.A. and Dines, T.D. (2002) New Atlas of the British and Irish Flora. Oxford University Press, Oxford.
   
4. Mabey, R. (1996) Flora Britannica. Sinclair-Stevenson, London.
   
5. Grigson, G. (1996) The Englishman’s Flora. Helicon Publishing, Ltd., Oxford.
   
6. Botanical.com (December 2003):
   http://botanical.com/botanical/mgmh/b/bogbea63.html