General – dark green, robust, unbranched, 4 – 15 cm tall or more; single-sexed, males have enlarged heads at plant tips, females produce sporophytes; lower portion covered by grey rhizoids.
Leaves – 6 – 10 mm long, lance-shaped, sharply pointed; spread at right angles when moist, erect-flattened and rolled when dry; membranous, sheathing base; edges coarsely toothed; midrib covered on inner surface with 20 – 55 vertical tiers of cells (lamellae) 4 – 9 cells high, each tier ends with U-shaped cell.
Sporophytes – common, at plant tips; stalk wiry, very long; capsules horizontal, 4- sided, 64 short, rounded teeth and expanded central membrane around capsule mouth; capsule hood has tuft of hair at tip, covers entire capsule.
In moist coniferous forests; widespread across Northwestern Ontario and boreal forests; cosmopolitan.
The hair-caps are the largest unbranched mosses in western Canada. Common hair-cap could be mistaken for alpine hair-cap (Pogonatum alpinum, also called Polytrichastrum alpinum), but that moss has round (not square) capsules. Tea made from common hair-cap was once taken to dissolve kidney and gall bladder stones. Based on the Doctrine of Signatures, this moss should be good for the hair, so a strong tea of common hair-cap was used as a rinse to ‘strengthen and beautify’ ladies’ tresses. The stems of common hair-cap often reach 30 – 45 cm or more in length. when the leaves are removed, the central stems form tough, pliable strands that have been used to make brooms and brushes or have been woven or plaited to make mats, rugs, baskets, and hassocks. Apparently this was quite an art in ancient Europe. A hair-cap moss basket from the remains of an early Roman fort at Newstead, England, dates from 86 AD.