Petalwort (Petalophyllum ralfsii)

GenusPetalophyllum (1)

Classified as Nationally Scarce in Great Britain and protected under Schedule 8 of the Wildlife and Countryside Act 1981. Vulnerable in Europe and listed under Appendix I of the Bern Convention, and Annex IIb of the EC Habitats and species Directive (2).

Petalwort is a tiny, delicate liverwort, with a flattened pale green thallus, featuring crisped raised projections called 'lamellae' (3), which radiate out from the thickened central mid-rib (4). These projections, which have something of a 'frilly' appearance, are just one cell thick, and are translucent (4). The base, which is tuberous, is embedded in the substrate (2).

All liverworts are named because the lobed species were thought to resemble the liver. During Medieval times, common belief held that the appearance of a plant indicated which part of the human body it could cure; liverworts were therefore thought to cure liver ailments (5).

This liverwort has a sparse distribution around the coastline of Britain; there are around 25 sites at present, and 4 are known to have been lost as a result of habitat destruction (3). A survey by Plantlife in 2002 found that populations in the south-west of England seem to be increasing, possibly as the result of the climatic trend towards a milder climate with wetter winters in that area (3). Populations in the rest of England seem to be remaining stable, and a known population in Wales was found to be much larger than previously thought, being larger than all other British populations put together (3).

Usually inhabits damp, calcareous sand in dune slacks in wet conditions, and may even be completely inundated with water in winter (2). A particularly suitable habitat seems to be the edges of paths that are slightly disturbed (2).

Liverworts, hornworts and mosses form a group of simple plants called bryophytes (2). Bryophytes lack many of the more complex structures of the higher plants, such as a vascular system, and flowers. They do not have roots, instead they have structures called 'rhizoids' which absorb water and anchor the plant to the substrate. In liverworts these rhizoids each consist of a single elongated cell (6). Like all plants, bryophytes have a life cycle consisting of two main parts, called the 'gametophyte' and 'sporophyte' generations. In bryophytes it is the gametophyte stage that is dominant (6). Plants in the gametophyte stage can reproduce sexually. Male organs (antheridia) produce sex cells, which move to the female organs (archegonia) in films of water; fertilisation occurs and a 'sporophyte' develops, which remains attached to the plant. The sporophyte releases spores, which disperse and develop into a new plant (6). Petalwort produces sporophytes from March to May, and usually disappears in winter, surviving in the form of tubers in the substrate (2).

This delicate liverwort faces a large number of threats, including habitat loss resulting from development and natural succession on dune slacks (3), unsuitable drainage, trampling by humans (7) and other recreational activities (2). Nutrient enrichment, resulting in unsuitable conditions for this species has occurred at some sites as a result of a large amount of dog fouling (3). Furthermore, reductions in grazing (2), as well as shading by tall vegetation and encroachment of scrub are also problems (3).

Petalwort is a UK Biodiversity Action Plan priority species, and has a species action plan to guide its conservation. It is also included in English Nature's Species Recovery Programme, which in conjunction with the Countryside Council for Wales has part-funded Plantlife to carry out research and survey work on this species (3). At present, most of the sites supporting this liverwort are protected (3).

For more information on this species see:

Plantlife Species Dossier:

Information authenticated by Plantlife, the wild plant conservation charity:

  1. National Biodiversity Network Species Dictionary (July, 2002)
  2. Church, J.M., Hodgetts, N.G., Preston, C.D. and Stewart, N.F. (2001) British Red Data Books: mosses and liverworts. Joint Nature Conservation Committee, Peterborough.
  3. Holyoak, D.T. (2002) Petalwort (Petalophyllum ralfsii): Report to Plantlife on work carried out in England and Wales during 2001 and 2002. Plantlife report number 202. ISBN 1 872613 73 X. Plantlife, London.
  4. Mosses and liverworts in Wales: Petalophyllum ralfsii. (July, 2002)
  5. Egerton, H. and Jones, F. (1998) Nature Encyclopedia. Dorling Kindersley, London.
  6. Mosses and Liverworts in Wales (July, 2002)
  7. UK BAP (July, 2002)