Haircap

Haircap is a term with several meanings, used in botany and in everyday language. In scientific and horticultural contexts, it most often refers to haircap moss, a group of mosses in the genus Polytrichum, particularly Polytrichum commune. These mosses are robust, tufted plants that commonly form green to brown mats in a range of habitats, including forests, wetlands, and tundra.

The name haircap moss reflects the characteristic appearance of the sporophyte. After the capsule develops on a relatively tall stalk (seta), the capsule is often surrounded by a dense rosette of long, hairlike leaves, which gives the plant a “hairy” look around the reproductive structure. The capsule is initially covered by a protective calyptra that resembles a cap; as spores mature, the calyptra detaches and the capsule releases spores.

Habitat and ecology: Haircap mosses are widespread in temperate and boreal regions and are common on acidic soils, forest floors, heathlands, and disturbed sites. They are desiccation-tolerant and contribute to soil formation, moisture retention, and microhabitat structure. In ecosystems they can act as pioneer species, helping to stabilize bare ground and influence nutrient cycling.

Other uses: In ordinary English, haircap can simply mean a cap worn over the hair, such as a shower cap or a medical/surgical cap, used to keep hair contained and protect hygiene in clinical or personal care settings.

See also: moss, calyptra, Polytrichum.