A perennial herb found on disturbed ground such as in gardens, shrubberies, felled woodland, waste ground, on walls and in pavement cracks. It spreads readily by seed, often colonising newly disturbed sites. It occasionally grows in semi-natural habitats, including marshes. 0?450 m (above Garrigill, Cumberland).
This species was first collected in 1891, but was unrecognised until the 1930s. It established itself most strongly in south-east England, and has spread rapidly north and west. The current map shows a dramatic extension from the 1962 Atlas and it is now one of our most frequent aliens.
Native of N. America; widely naturalised in C. & N. Europe.
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