P. trichoides is found in a range of still or slowly flowing, mesotrophic or eutrophic waters including lakes, ponds, rivers, canals, ditches and flooded mineral workings. It often colonises disturbed sites such as recently cleared canals and ditches. Lowland.
Although the distribution of this elusive linear-leaved pondweed is better known now than at the time of the 1962 Atlas, it is probably still under-recorded as it is difficult to recognise, especially when growing with P. pusillus. There is evidence of a genuine increase in frequency since 1960 in the Somerset Levels, perhaps because of eutrophication.
Eurosiberian Southern-temperate element.
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Light (Ellenberg): 6
Moisture (Ellenberg): 12
Reaction (Ellenberg): 7
Nitrogen (Ellenberg): 6
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 3.8
July Mean Temperature (Celsius): 16.2
Annual Precipitation (mm): 739
Perennation - primary
Life Form - primary
Clonality - primary
Count of 10km squares in Great Britain: 185
Count of 10km squares in Ireland: 0
Count of 10km squares in the Channel Isles: 1
Atlas Change Index: 0.57
Scarce Atlas Account
Potamogeton trichoides Chain. & Schldl.
P. trichoides is found in shallow, still or slowly-flowing water in a wide range of habitats, including lakes, reservoirs, ponds, lowland rivers, canals, drainage ditches and flooded clay, sand and gravel pits. It is usually found in meso-eutrophic or eutrophic water, often with Elodea canadensis or E. nuttallii and frequently with Myriophyllum spicatum, Potamogeton crispus and other linear-leaved pondweeds, especially P. pectinatus and P. pusillus. In some sites it has been noted as an early colonist of freshly cleared canals and ditches. It is confined to the lowlands.
P. trichoides is an annual which flowers and fruits sparingly. New colonies are probably established by seed, but reproduction in established populations is primarily by turions, which develop throughout the summer on the ends of stems and branches.
This species is one of the less conspicuous linear-leaved Potamogeton species, a group which is troublesome to identify and often avoided by botanists. Although it was first recognised in Britain in 1850, many early records were erroneous (Dandy & Taylor 1938). It is almost certainly under-recorded in some areas, but plants of P. pusillus are sometimes misidentified and reported as this species. A few years ago it was thought to be declining, but there have subsequently been many new records and there is little doubt that it was simply being overlooked. In some areas it may actually be increasing: these include the Somerset Levels, where it was first recorded in 1972 and is now locally abundant.
P. trichoides is widespread in Europe, north to Scotland and southern Sweden. Its world distribution is more southerly than that of P. friesii or P. praelongus: it is found in western and central Asia and eastern and southern Africa.
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.