Native populations of this perennial herb are found in calcareous, meso-eutrophic lakes, ponds and ditches. Alien colonies occur in a range of other habitats, including canals. All our plants are female, reproducing vegetatively. Lowland.
Native or alien (change +1.65). This species was first recorded in 1633, and the presence of only one sex suggests that it may not be native (Cook & Urmi-König, 1983). In Britain apparently native populations have been in long-term decline, probably due to eutrophication. Alien populations are often short-lived. Forbes (2000) argues that it may be native in Co. Fermanagh.
Eurosiberian Boreo-temperate element; widely naturalised outside its native range.
Scarce Atlas Account
Stratiotes aloides L.
S. aloides is a characteristic dominant in the submerged layer of a macrophyte community with Ceratophyllum demersum and Utricularia vulgaris where Callitriche platycarpa, Hydrocharis morsus-ranae and Lemnaceae form a floating mat on the surface. Other scarce species which may be present in this community include Potamogeton compressus and Sium latifolium. S. aloides grows in the still water of grazing marsh ditches, appearing to prefer water that is moderately rich in nutrients and calcareous. It is most often found where there are enhanced levels of calcium, magnesium and inorganic nitrogen, notably towards the upper margin of the fen basin (Wheeler & Giller 1982), S. aloides grows where regular cleaning of the ditches or ponds (often with grazing of the margins) suppresses the growth of reed and other tall emergents. It requires well-lit conditions, and is absent from turbid water or where bank vegetation and dense emergent growth shade the water surface. Outside its relict native range, S. aloides has been widely introduced into ponds and lakes. It is confined to sites below 50 metres in the warm lowlands.
S. aloides is free-floating and stoloniferous. In Britain it reproduces only by offsets and fruit are never set, since the species is dioecious and only the female plant is found here. When introduced as whole plants into a new site, S. aloides increases rapidly. However, without seed it is unable to spread naturally from one drainage system to another.
The native range of S. aloides has contracted sharply in the last 150 years. However, in The Netherlands S. aloides has increased, apparently favoured by nitrogenous fertiliser run-off from farmland (Westhoff & Held 7969). The decline in Britain may follow the rise in phosphate content of the water from sewage, farm slurry or detergents. S. aloides is now only frequent in Broadland, and has largely disappeared from its previous strongholds in the Cambridgeshire Fens, Lincolnshire and Yorkshire. However, due to its attractive appearance S. aloides is often grown in ponds and can be encountered as a casual introduction throughout lowland Britain. It can spread rapidly in water with a low phosphate level and in some sites, such as the Sussex Pevensey Levels, it is thoroughly naturalised.
S. aloides is widespread in the temperate and warmer parts of Europe and western Asia, though rare in the far south and west. For example, it is absent from both Greece and Portugal.
J. O. Mountford
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.