any of the plants of the genus Grimmia (subclass Bryidae), which includes more than 100 species distributed throughout the world, primarily on rocks or stone walls. A few species grow on roofs or in streams; G. maritima forms cushions up to four centimetres (1 ¹/₂ inches) tall on rocks along seashores. Nearly 50 species of Grimmia are native to North America, and about 30 are found in Great Britain. Most fringe mosses are one to three centimetres tall and have blackish-green, lance-shaped phyllids (leaves) about two millimetres (¹/₁₂ inch) long, which are sometimes tipped with a white hair.