Sunny, usually sterile or disturbed soil, in areas that dry out rapidly. Common in urban areas, on stone or concrete walls, on road margins, even on rooftops. Sometimes forming extensive stands on roadside banks, most frequently at lower elevations but extending to alpine sites; infrequent in the wettest oceanic climates of the open coast. World Distribution
Widespread at all latitudes, especially in temperate or colder climates, from the high arctic to antarctic. At tropical latitudes more frequent in urban areas or at higher elevations.