An annual of hedgerows, dry roadside-banks and wall-tops, especially close to the sea, but spreading to roadside verges, rubble heaps, railway ballast and waste ground. It is also a garden and street weed. Colonies may be very persistent, even where the species is confined to weedy habitats. Lowland.
G. rotundifolium has increased markedly since the 1962 Atlas. As a presumed native it is restricted to S. Britain and the extreme south of Ireland. However, given its spread in parts of S. England, it is possible that some recent, supposedly alien, records to the north of this could in fact represent a natural extension of its native range.
Eurosiberian Southern-temperate element; widely naturalised outside its native range.