This rhizomatous perennial herb is found in shallow, calcium-rich but nutrient-poor waters in lakes, pools, clay-pits, shallow streams and ditches. It grows over a range of substrates, including peat, marl, sand and clay. Lowland.
P. coloratus has declined over much of its British range, having been lost from many sites because of drainage or eutrophication. Many remaining localities are in nature reserves. It has, however, also colonised some new habitats since 1930, and the largest populations are currently those in abandoned brickfields in Peterborough. In Ireland it is still relatively frequent in the central plain.
European Southern-temperate element.
Light (Ellenberg): 7
Moisture (Ellenberg): 11
Reaction (Ellenberg): 8
Nitrogen (Ellenberg): 5
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 4.1
July Mean Temperature (Celsius): 15.1
Annual Precipitation (mm): 893
Perennation - primary
Life Form - primary
Clonality - primary
Clonality - secondary
Count of 10km squares in Great Britain: 142
Count of 10km squares in Ireland: 140
Count of 10km squares in the Channel Isles: 2
Atlas Change Index: 0.03
Scarce Atlas Account
Potamogeton coloratus Hornem.
This aquatic species is usually found in shallow, base-rich but nutrient-poor water. It grows in pools and ditches in calcareous fenland, in slow-flowing streams, in flooded clay and marl pits and in lakes on limestone or at the landward edge of calcareous sand dunes. In fens it can also be found growing sub-terrestrially on damp moss carpets. It is found over a range of substrates including peat, clay and fine or stony sediments derived from limestone. Charophytes, including Chara hispida, C. pedunculata and C. vulgaris, are often found growing with it. It is a lowland species, notably absent from the more elevated Carboniferous limestone areas of northern England where there are many apparently suitable habitats.
P. coloratus is a rhizomatous perennial. The rhizome system allows it to persist through brief periods when its habitat dries out. It flowers freely in shallow water and produces numerous seeds. Little is known of the conditions under which it reproduces by seed. At some fenland sites it has reappeared following disturbance of peat (e.g. in pools created when invasive shrubs were extracted), which suggests that the seeds can retain viability for some years in moist peat.
A number of P. coloratus sites have been lost through drainage or eutrophication. Many of its remaining localities are species-rich calcareous wetlands which are nature reserves or SSSIs. These are presumably safeguarded from habitat destruction but are probably not immune from the more insidious effects of a falling water table or nutrient enrichment. In addition, P. coloratus has colonised some newly available habitats and it is, for example, locally frequent in flooded brick-pits in the Peterborough area.
It is found in western, central and southern Europe, extending north to Scotland and southern Sweden. Outside Europe it is known only from north-western Africa and south-western Asia. It is listed as a most vulnerable species in The Netherlands.
The species of Potamogeton have often been misidentified, and many older records are erroneous. Records made before 1940 have been accepted for these maps only if supported by expertly determined herbarium specimens. The maps must consequently under-estimate the former distribution of some species.
C. D. Preston