Species Focus - Common Haircap (Polytrichum commune)

Polytrichum commune is a widespread and familiar sight, forming sizable patches of miniature dark green forests in damp habitats including woodlands, ditches and open hillsides.

It is one of our largest mosses with tough wiry stems that grow up to 40cm tall. Its large size is accompanied by interesting adaptations not seen in other unrelated bryophytes. It has specialised water conducting tissue to transport water from the base of the plant. Its spirally arranged dark green pointed leaves are also thicker than those of most other mosses. The upper surfaces are covered with ridges of photosynthetic cells which trap moist air allowing photosynthesis to take place whilst minimising water loss.

Polytrichum species are known as ‘Haircaps’ for the hairy calyptra that covers the capsule, produced during the summer months. The 4 angled, boxy capsule with a constriction below distinguishes P. commune from P. formosum which is similar in appearance and can occupy similar habitats but whose capsule lacks the constriction. 

However, greater familiarity with these mosses as well as some skill and patience in producing cross sections of the leaves for microscopic examination may be necessary to identify some specimens. Please submit your records, preferably with photos, to the Cofnod ORS or the LERC Wales App.