Cornish Biodiversity Network  -  Supporting Wildlife Recording

   A B C D E F G H I J K L M N O P Q R S T U V W X Y Z restore

Cornish Red Data (2009)

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.

Riccia rhenana - Pond Crystalwort

Range & Status

Mainly a C. European species, ranging from Portugal, France, Belgium and Switzerland north to S. Sweden and Russia; also SW. Asia, Siberia and N. America. First recorded in Britain in 1952 and now known in a few scattered localities from N. Wiltshire and Surrey to W. Norfolk and Cheshire, with an isolated site in W. Cornwall. This liverwort is grown by aquarists and Preston (in Hill et al. , 1991) suggests that the British records all result from deliberate or accidental release of cultivated material. The Cornish site is in rather

inaccessible ponds in the middle of a wood, where direct introduction seems rather unlikely.

Regional Distribution

One site in W. Cornwall (Pendarves Wood, SW63N), where it was discovered in 1994 (Long, 1995) and was still present in 1998.

Habitat & Ecology

Grows mainly as an aquatic plant, floating on and just below the surface of shallow water in pools, often mixed with duckweeds ( Lemna spp.). It also persists as a modified form on wet mud when the water level falls. At Pendarves Wood it occurs in a small pond that is partly shaded by trees. It is a dioicous species for which sporophytes are unknown.


It might eventually be lost from the pond at Pendarves Wood if shading from surrounding trees increases.


The Pendarves Wood site is within a reserve managed by Cornwall Wildlife Trust. The species is not placed on the UK Red-list because it is suspected as having been introduced into Britain.


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.