In Iceland, tundra is largely confined to the interior that has very short summers as well as extensive sands interspersed with stretches of wetlands along rivers. The barrens in the central highlands of Iceland have very sparse vegetation. The species growing there are well adapted to the short summer. The plants need to tolerate drifting sand and extreme soil conditions. Some of the species form dense cushions. Among them are Moss Campion (Silene acaulis) and Tufted Saxifrage (Saxifraga caespitosa), while Thrift (Armeria maritima) forms a smaller rosette. Moss Campion forms a dense cushion with small but fragrant pink flowers. When the flowers are absent the bright green leaves in the cushion are more pronounced. Tufted Saxifrage carries white flowers. This species is widespread in Iceland. Thrift carries a rosette of fleshy leaves. Grasses, rushes and sedges grow as stoloniferous or tussock-forming species on the tundra sand. These species depend on vegetative growth for many years but also reproduce sexually. Facilitation may occur when aggregations of some species, for example, Moss Campion, form cushions that provide shelter or otherwise suitable conditions for the establishment of other plant species. Plants of the barrens growing as perennial rosettes, cushions and tussocks may reproduce by seed and disperse into new sites in the vast sands of the interior.