A rhizomatous perennial of calcareous and often rather eutrophic, still or very slowly flowing waters. These include lakes, sluggish rivers and streams, canals, fenland lodes and flooded mineral workings. Lowland.
P. friesii expanded through the canal network, and subsequently declined as canals became disused or dominated by pleasure boat traffic. Like other linear-leaved pondweeds it is probably under-recorded. The distinction between P. friesii and P. pusillus is straightforward in England but becomes difficult in N. Scotland and some records may require reassessment.
Circumpolar Boreo-temperate element, with a disjunct distribution.
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Light (Ellenberg): 7
Moisture (Ellenberg): 12
Reaction (Ellenberg): 7
Nitrogen (Ellenberg): 5
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 3.6
July Mean Temperature (Celsius): 15.4
Annual Precipitation (mm): 782
Perennation - primary
Life Form - primary
Clonality - primary
Count of 10km squares in Great Britain: 270
Count of 10km squares in Ireland: 43
Count of 10km squares in the Channel Isles: 0
Atlas Change Index: -1.06
Scarce Atlas Account
Potamogeton friesii Ruff.
Status: not scarce
This species grows in still or slowly-flowing water. In England and Wales its main habitats are lowland rivers, canals, fenland lodes and species-rich ditches in grazing marshes. Here it grows with species such as Ceratophyllum demersum, Potamogeton crispus, P. pectinatus, P. perfoliatus, P. pusillus and Ranunculus circinatus. In Scotland it is also found in canals in the industrial lowlands, but most records are from lakes where the water is enriched by bases derived from limestone, calcareous sand dunes or calcareous glacial drift. It is a characteristic species of the ‘machair lochs’ on the west coast of the Outer Hebrides. It is usually found in relatively eutrophic water, but it is unable to withstand very high levels of dissolved nutrients. It is confined to the lowlands.
P. friesii is a non-rhizomatous species which flowers and fruits rather sparingly. Its normal mode of reproduction and dispersal is by turions, which develop in the leaf axils and at the end of short axillary branches in July and August.
This species was recorded in the 19th century in a number of canals in southern England which have now disappeared from the landscape. In some other canals which are still extant, and in some rivers in this area, it has not been recorded since before 1950. Since 1950 there have been few further losses in southern England, where its tolerance of eutrophic water and its ability to persist in canals and fenland lodes which carry light boat traffic is advantageous. It appeared in the Thurne Valley broads in the 1930s, when the charophyte communities in the calcium-rich but hitherto nutrient-poor lakes were replaced by vegetation dominated by vascular plants as nutrient levels increased. However, it was unable to persist when nutrient levels increased even further (George 1992). It sometimes colonises newly available habitats, such as flooded gravel pits. It is extinct in Balgavies Loch and Rescobie Loch, where the aquatic flora has also been greatly impoverished by eutrophication (Ingram & Noltie 1981).
It is a widespread species, which has a predominantly northern distribution in Europe and is also found in Asia and North America.
C. D. Preston
Atlas text references
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.
1994. Scarce plants in Britain.