Cornish Biodiversity Network  -  Supporting Wildlife Recording

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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.

Petalophyllum ralfsii - Petalwort

Range & Status

(syn. P. ralfsii (Wilson) Nees & Gottsche ex Lehm.). Widespread around the Mediterranean, including N. Africa and Turkey; extending along the Atlantic seaboard of Europe northwards to Britain. An allied species occurs in eastern U.S.A. In Britain, occurs in widely but very sparsely scattered localities around the coasts, on the west coast from Cornwall to W. Ross, on the east coast from Norfolk to N. Northumberland.

Regional Distribution

Occurs at several nearby sites in each of two sand dune areas on the north coast; in the Hayle Harbour to Gwithian Towans area, and on and near Gear Sands. Most of its populations occupy small areas and some consist of few plants, but ca 228,000 thalli on the Triangular Spit at Hayle Harbour comprise around 20% of the entire UK population.

Habitat & Ecology

Grows in sparsely vegetated to almost bare places on damp calcareous sand in sanddune areas, typically at the edge of dune-slacks, but also on edges of paths and in similar open sites. It appears to be intolerant of heavy trampling or of shading by taller plants. It is most conspicuous in winter and spring, becoming almost invisible in summer when it perennates by means of underground tubers. It is a dioicous species, but capsules are frequently produced from December to May.


The Cornish populations remain susceptible to adverse effects of small-scale habitat changes. The open sites required by the species are mostly maintained by rabbit grazing, trampling, or both, while the availability in winter of the damp sandy substrata it needs is dependent on the hydrology of the dune slacks. Several of its sites are close to large holiday camps and thus potentially at risk from increased pedestrian traffic, or other activities. Eutrophication from excessive inputs of dog dung has led to disappearance of small populations near access points onto Upton Towans over the past decade.


Some of the Cornish populations are within SSSI. Although the species is recorded (post-1950) from 18 10km squares in Britain it appears to be declining and often occurs in very small quantity. Hence it is placed on Schedule 8 of the Wildlife and Countryside Act 1981, as amended and covered by the UK BAP and the Species Recovery Programme of Natural England. It is also protected under Annex II of the EC Habitats Directive, listed on Appendix I of the Bern Convention, and listed as Vulnerable under the IUCN Red List. Over the past decade Plantlife International has surveyed its populations regularly in Cornwall and elsewhere, and published guidance on its conservation. A detailed Species Dossier can be downloaded from the Plantlife International website.


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.

Cornish Biodiversity Network. 2017.