A biennial of damp places, such as ditches and river banks, and of drier habitats, including rough grassland, waste ground, rubbish tips and roadsides. It is a colonist of disturbed areas, particularly on dredged mud, sometimes forming large stands. Generally lowland, but reaching 305 m at Llynheillyn (Rads.).
The distribution of C. maculatum is little changed since the 1962 Atlas, although the map suggests declines on the edges of its range. Conversely, local increases in its core areas have been reported, particularly in open habitats (Killick et al., 1998).
As an archaeophyte C. maculatum has a Eurosiberian Southern-temperate distribution; it is widely naturalised outside this range.
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