polytrichum

Polytrichum is a genus of mosses in the family Polytrichaceae, commonly known as haircap mosses. The genus comprises about 60 species distributed across boreal and temperate regions worldwide. Polytrichum forms dense, tufted mats with tall, erect shoots that can reach several centimeters in height, giving the plants a conspicuously bristled appearance in sunlit patches.

Leaves are crowded along the stems and are stiff, with a strong central costa. The upper leaf surface bears lamellae—rising ridges of thickened cells—that give the leaf a shiny, striped look and aid in water retention. The leaves taper to a fine tip, and the plant generally presents a robust, evergreen appearance.

Reproduction occurs via a conspicuous sporophyte that rises from the female gametophyte. A long seta supports a cylindrical to ovoid capsule, often crowned by a calyptra. In many species the capsule opens irregularly and releases spores through the operculum and peristome teeth. Sexual structures arise on separate plants in many species, and reproduction requires moisture to transport sperm to archegonia.

Habitat and ecology: Haircap mosses are common in acidic, nutrient-poor soils, peatlands, forest floors, and open, disturbed sites. They tolerate dehydration and resume growth quickly after rain. Their dense mats retain moisture, influence soil microhabitats, and contribute to early-stage soil formation. Some species are used as indicators of undisturbed or mature habitats and are collected for horticultural use.