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; an Eurasian Temperate species. It grows on the River Shannon in Ireland. It was formerly known on the Rivers Thames, the Medway and the Arun, but it can now be seen at only one site on the River Tamar, on the Devon bank.
Almost certainly extinct on the Cornish side of the River Tamar, it was last recorded near Calstock in 1958 (SX46). It remains on the Devon side where a small patch was seen in 1995. It has also been re-introduced, by the Environment Agency, on the Devon bank.
Habitat & Ecology
An estuarine plant of tidal mud. It appears to be restricted to a very narrow zone within
The causes of its decline are uncertain - it may be unable to compete with coarse growing plants such as Common Reed Phragmites australis , or be affected by sewage effluent or may even be overgrown by its own hybrids.
Most of the Cornwall side of the River Tamar bank near Calstock is unprotected.
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.