Like E. hexandra, this is an annual which grows in shallow water or on damp mud or silty sand exposed at the water`s edge. Unlike that species it is confined to mesotrophic or eutrophic habitats. Lowland.
Although E. hydropiper has disappeared from S.E. England (last recorded 1944), it was first recorded in Scotland in 1968 and has since been found in many more sites there. Mitchell (1981) suggests that it has been spread by birds, but it is possible that, like the equally inconspicuous E. hexandra, it may have been under-recorded in the 1962 Atlas. In Ireland its distribution has remained stable.
Eurosiberian Boreal-temperate element, with a continental distribution in W. Europe.
Height (cm): 5
Perennation - primary
Life Form - primary
Comment on Life Form
Clonality - primary
Clonality - secondary
Count of 10km squares in Great Britain: 33
Count of 10km squares in Ireland: 19
Count of 10km squares in the Channel Isles: 0
Atlas Change Index: 0.66
Scarce Atlas Account
Elatine hydropiper L.
This aquatic plant colonises bare mud and silty sand above and below the water surface. In clear water, E. hydropiper can germinate in depths of up to 0.75 metres. When exposed or lightly covered by water, the compact plants root at every node, but in deeper water the elongated stems take on a straggly growth form as they reach upwards towards the light. It is restricted to a narrower range of trophic conditions than the closely related E. hexandra, having never been known to occur in the oligotrophic waters of Lakeland or the Scottish Highlands for example. The most frequently noted associates are Callitriche hermaphroditica, C. stagnalis, E. hexandra, Eleocharis acicularis, Littorella uniflora and Lythrum portula. It is confined to the lowlands.
E. hydropiper is a self-fertilising annual, although there seems no reason why cross-pollination by insects visiting open flowers should not take place. Prolific seed production occurs in exposed plants. Long range dispersal is almost certainly assisted by seeds becoming embedded in mud adhering to water fowl. Buried seeds may remain dormant in the mud for many years, until stimulated by increased light intensity brought about by abnormally low water levels during the summer months.
Population trends in Britain are difficult to assess, as the species has more than once been reported to have been lost from a locality, only to reappear in abundance when conditions for germination became more favourable. Nevertheless, its recent retraction of range in England and expansion in Central Scotland is undoubtedly real. The principal threat is from excessive eutrophication of the habitat, particularly from agricultural fertilisers, transforming the water bodies' firm substrate into a soft ooze. Premature dieback and eventual loss of one well-established and large colony on drying-out mud was suggestive of some form of metal ion toxicity.
It is found in northern and central Europe, only locally extending cast and south, and in North America.
E. hydropiper grows in brackish water in some north European countries, but it has not been found in this habitat in Britain.
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.
1997. Aquatic plants in Britain and Ireland.
1994. Scarce plants in Britain.