A perennial herb of shallow, clear, base-rich water which may grow in lakes and rivers, but is more frequent in smaller waters such as streams, canals, ditches and ponds. It rarely colonises newly available habitats, although it is sometimes found as an introduction in ponds. Generally lowland, but reaching 380 m at Malham Tarn (Mid-W. Yorks.).
G. densa has declined in Britain due to urbanisation, which has led to its loss from the London area, eutrophication and the loss of spring-fed streams and ditches because of falling water tables. This decline began before 1930, but is still continuing.
European Temperate element.
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Light (Ellenberg): 8
Moisture (Ellenberg): 12
Reaction (Ellenberg): 8
Nitrogen (Ellenberg): 5
Salt Tolerance (Ellenberg): 1
January Mean Temperature (Celsius): 3.7
July Mean Temperature (Celsius): 15.9
Annual Precipitation (mm): 750
Perennation - primary
Life Form - primary
Clonality - primary
Clonality - secondary
Count of 10km squares in Great Britain: 590
Count of 10km squares in Ireland: 42
Count of 10km squares in the Channel Isles: 0
Atlas Change Index: -1.23
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.
1965. Vergleichende Chorologie der zentraleuropäischen Flora. Volume 1. 2 vols.
1995. Pondweeds of Great Britain and Ireland. Botanical Society of the British Isles Handbook no. 8.
1997. Aquatic plants in Britain and Ireland.