A morphologically variable, rhizomatous perennial. In the lowlands, robust plants grow on river banks and the margins of lakes, mires and reed-swamps. In its upland sites, it is a shorter plant and often grows on deep, wet, gently sloping peat. 0-975 m (Glas Maol, Angus).
Because of better recognition and recording, C. aquatilis is now known from very many more 10-km squares than it was in the 1962 Atlas, although it may remain overlooked in some areas.
Circumpolar Boreo-arctic Montane element; absent from mountains of C. Europe.
Light (Ellenberg): 8
Moisture (Ellenberg): 10
Reaction (Ellenberg): 4
Nitrogen (Ellenberg): 3
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 2.3
July Mean Temperature (Celsius): 13.2
Annual Precipitation (mm): 1255
Height (cm): 110
Perennation - primary
Life Form - primary
Life Form - secondary
Clonality - primary
Count of 10km squares in Great Britain: 219
Count of 10km squares in Ireland: 39
Count of 10km squares in the Channel Isles: 0
Atlas Change Index: 0.76
Scarce Atlas Account
Carex aquatilis Wahlenb.
Status: not scarce
This is a species of mires and swamps. In lowland lake basins it frequently forms large stands with Carex rostrata, C. vesicaria and Equisetum fluviatile at the upper end of the basin. It can be dominant in swamps alongside slow-flowing rivers, with Carex acutiformis, C. vesicaria, Phalaris arundinacea and Phragmites australis. In upland areas it is found on gently sloping mires on deep peat, with Carex curta, C. nigra, C. rariflora, C. rostrata and several Sphagnum species and bryoid mosses. It also occurs by drainage channels in upland mires and occasionally alongside fairly fast flowing upland rivers. In these habitats plants are notably shorter than those in the lowlands. It has a wide altitudinal range from sea-level to 750 metres on Glas Maol.
It is a rhizomatous perennial. The rhizome is far-creeping and the plant therefore has a considerable potential for vegetative spread. Plants are often sterile over large areas, especially where populations are shaded or where there have been changes in water level. C. aquatilis is wind pollinated and hybridises readily with other members of the C. nigra group. Many populations appear to be hybrid swarms.
Some lowland populations are disappearing due to land-use changes, but those in the Scottish Highlands are not threatened except very locally in areas selected for ski developments where ski-tows and downhill running could be detrimental.
This is a circumpolar species. In Europe it extends south to Wales, northern Germany and central Russia but in western North America it occurs as far south as Arizona and California.
A. C. Jermy