A perennial herb of dry, undisturbed and open habitats on skeletal, or virtually non-existent, acidic or basic soils. Typical natural habitats include shingle, sand dunes, cliffs and steeply sloping, S.-facing rocks. It is also frequent on walls, roofs, gravel tracks, pavements and road verges. It is resistant to grazing. 0-500 m (Arncliffe, Mid-W. Yorks.), with an exceptional record at 845 m on Great Dun Fell (Westmorland).
This creeping perennial herb grows on open, dry sites, such as limestone rocks, walls, roofs, the concrete of old airfield runways, maritime shingle, paths and gravel on graves. 0-570 m (Hartside, Cumberland).
A perennial herb found as a garden escape or throw-out on roadsides and other waste grassy places. Lowland.
This creeping perennial herb of base-poor substrates occurs on rocks, dunes and shingle, and is also known from dry grassland. It is a characteristic plant of open ground on acidic rock outcrops near the sea. It also grows on old walls, rocky hedge banks, and quarries and mine spoil on acidic substrates. 0-1080 m (Snowdon, Caerns.).
A small perennial herb with ascending stems readily rooting at the base which provide an anchorage to the crumbling surfaces of old walls on which it characteristically grows. Other habitats include quarries, cemeteries and limestone rocks. Lowland.
A mat-forming perennial herb of open, dry, well-drained habitats, including rocks and screes, wooded cliffs and gullies. Naturalised colonies are found in churchyards, on waste ground, mine waste, walls and railway land. Lowland to 600 m as native (Llyn y Fan Fach, Carms.).
A small monocarpic or short-lived perennial herb, naturalised on walls, gravel pits and stony waste ground. Lowland.
An evergreen, mat-forming perennial which is found as a well-naturalised garden escape on dry, sunny roadsides. Lowland.
A rhizomatous perennial herb which grows on sea-cliffs and in mountains in rock crevices and on moist rock ledges. Very rarely, in W. Ireland, it occurs on coastal limestone pavement. In montane habitats it usually occupies sites which are at least slightly base-enriched. Although descending to sea level in N.W. Britain and Ireland, it is usually found above 300 m, reaching 1160 m on Ben Lawers (Mid Perth).
A perennial herb growing on old walls, rock outcrops, roadside banks and waste ground. Generally lowland, but reaching 365 m in N. Wales, and recorded at 845 m on Great Dun Fell (Westmorland).