The descriptive text, below the map, is from the Cornish Red Data Book (2009). The map on this web page depicts the organisms distribution and shows the records made pre-2000 and those made since.
Range & Status
Native. European Temperate species. Mainly found in the western half of the British Isles.
Found in the natural water-bodies of Dozmary Pool (SX17) and Loe Pool (SW62) and more recently in man-made reservoirs including Colliford (SX17), Cargenwen (SW63) and Drift (SW42). It is probably still present in other reservoirs such as Stithians (SW73) and Siblyback (SX27) where it has been recorded before 1999. It occurred in Abbey Pool, Tresco (SV81) on the Isles of Scilly until at least 1990, and there is no reason why it may not still be present.
Habitat & Ecology
Easily overlooked, it grows in the shallower water at the edge of fresh-water lakes and reservoirs. In Scilly it grew on the muddy edge, and in deeper water, of a slightly brackish pool.
Changes in water quality and possibly salinity. Around Stithians (SW73), Colliford and Siblyback reservoirs (SX17), the alien Crassula helmsii has become locally abundant which may swamp out plants of bare reservoir edges.
Possible clearance of Crassula helmsii .
I.J. Bennallick, S. Board, C.N. French, P.A. Gainey, C. Neil, R. Parslow, A. Spalding and P.E. Tompsett. eds. 2009. Red Data Book for Cornwall and the Isles of Scilly. 2nd Edition.Croceago Press.
The Cornish Red Data Book Project was led by the Cornwall and Isles of Scilly Federation for Biological Recorders (CISFBR). The full text and species accounts (minus the maps) are available on the CISFBR website.