A small, rhizomatous fern growing on the edges of non-calcareous lakes, reservoirs, ponds or slow-flowing rivers, and sometimes on damp mine workings or as a submerged aquatic. It requires areas where competition is reduced by fluctuating water levels or disturbance. 0-450 m (Pant-y-llyn Hill, Brecs.).
P. globulifera was lost from many sites before 1930 due to habitat destruction. Eutrophication and reduced disturbance have led to further losses in E. Britain and Ireland. In the west, many new sites have been found since 1980. It has been re-introduced to some former native sites (e.g. Rum).
Suboceanic Temperate element.
Count of 10km squares in Great Britain: 312
Count of 10km squares in Ireland: 24
Count of 10km squares in the Channel Isles: 3
Atlas Change Index: -0.03
External Species Accounts
Scarce Atlas Account
Pilularia globulifera L.
This fern is predominantly a lowland plant of silty or peaty lake and pond margins and shallow pans and pools resulting from brickearth or gravel extraction. It is an opportunist species, requiring open substrate which it will rapidly colonise, eventually to be ousted as the hydrosere progresses. It also colonises bare mud exposed by falling water levels. Characteristic associates include Apium inundatum, Hydrocotyle vulgaris, Ranunculus flammula and Samolus valerandi. Occasionally it maintains itself in denser plant communities as a submerged aquatic in base-poor pools around pH 6.0 and as a mire species with Calliergon cuspidatum and other hypnoid mosses, Carex diandra and Menyanthes trifoliata. In many sites competition may be kept to a minimum, and thus P. globulifera maintained, by cattle or horse trampling (poaching).
P. globulifera is a perennial species. Viable ‘pills’ (sporocarps containing sporangia) are formed in most populations except those in permanent deep water. They appear to have the potential of long-term storage in mud or silt but there is no evidence that this does happen. Spores released from the sporocarp in late summer can develop through the gametophyte phase to produce new sporophytes within seventeen days.
The number of lost sites reflects the changes in land-use that have taken place, especially between 1918 and 1950. Some of those that remain are probably stable; the species may disappear from others as a result of successional changes but these losses will perhaps be balanced by the colonisation of new sites. Populations can vary considerably in number from year to year, and plants can be particularly abundant in lakes and reservoirs in seasons when the water levels are exceptionally low.
This species is endemic to western Europe, with lowland areas in Britain, France, northern Germany and southern Sweden containing the bulk of the populations and outliers extending to Czechoslovakia, Italy and Portugal (Jalas & Suominen 1972), It is decreasing in much of mainland Europe and the British sites are therefore particularly important in a European context.
A. C. Jermy
PLANTATT - Attributes of British and Irish plants. (.zip 1455KB) This dataset was compiled and published in 2004, and last updated in November 2008. Download includes an Excel spreadsheet of the attributes, and a PDF explaining the background and nomenclature. Note that the PDF version is the booklet as published, whereas the Excel spreadsheet incorporates subsequent corrections. A hardcopy can be purchased from the Centre for Ecology and Hydrology.
Atlas text references
1988. The Irish Red Data Book. 1. Vascular Plants. .
1986. Atlas of north European vascular plants north of the Tropic of Cancer. 3 vols.
Jalas & Suominen (1972) .
1978. Ferns and their allies. The Island of Mull: a survey of its flora and environment. :12.1-12.7. .
1997. The ferns of Britain and Ireland, edn 2. .
1997. Aquatic plants in Britain and Ireland. .
1999. A Scottish perspective on the conservation of pillwort. British Wildlife. 10:297-302. .
1994. Scarce plants in Britain.