A shortly rhizomatous perennial herb of very wet, neutral to base-rich mires. It grows particularly well in silty, calcareous mud and by the edges of lime-rich flushes and springs. Although it occurs at sea level, many sites are at moderate or high altitudes, ascending to about 1000 m on Ben Lawers (Mid Perth).
C. dioica declined dramatically in lowland England before 1930, due to drainage and agricultural improvement. There have been further losses there (half the remaining sites south of the Severn-Humber line), but there are now a very substantial number of new records from N. and W. Britain, and from Ireland.
Circumpolar Boreo-arctic Montane element.
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