An annual to perennial herb of damp, bare sites, often found in open woodlands or hedgerows, or by shaded streams from where it may be washed downstream to new sites. Predominately lowland, but reaching 425 m at Dockray (Cumberland).
C. sibirica was cultivated in Britain by 1768 and was first noted in the wild in 1838. It has spread rapidly since 1930; in Cornwall, for example, it was not recorded until the 1930s but is now known in almost every 10-km square. It can quickly colonise woodland, suppressing other vegetation by its lush mass of spring foliage which then flops over nearby plants.
Native of eastern Asia and western N. America; widely naturalised in N.W. Europe.