Run your eye across a patch of broom fork-moss and the whole cushion seems to lean. Every leaf curves the same way, as though a draught had passed through and swept them flat, and that combed, all-one-direction look is the surest way to know it on sight. It is among the handsomest of the woodland mosses, and one of the most asked-for by people building terrariums and moss gardens.
Recognising it
Dicranum scoparium builds deep, rounded cushions of upright shoots, each shoot thickly clothed in long, narrow leaves that taper to a fine point. The giveaway is the set of those leaves: instead of standing out evenly all round the stem, they curve to one side in a smooth sweep, so that even on a still day under cover the cushion looks brushed by wind. The colour is a rich mid to dark green, drying a shade paler with a faint sheen, and a mature cushion is deep enough to lose a fingertip in. Its specific name, scoparium, means broom-like, for the way the swept shoots call to mind the worn head of a besom.
Where it grows
This is a moss of acid ground in shade. It carpets the floor of oak and birch woods, mounds over rotting logs and the swollen bases of trees, and spreads across peaty banks, heath and the tops of boulders wherever a skin of acid humus has gathered. Lime it will not tolerate, so chalk downland and mortared walls are the wrong places to look. Through the cooler temperate world it is common and widely spread, often keeping company with bun moss and the haircaps in the same sour, shaded conditions; learning the three together teaches your eye the whole acid-woodland palette.
Where the name comes from
The fork in fork-moss has nothing to do with the leaves and everything to do with the fruit. When Dicranum ripens its spores it raises curved capsules on tall yellow stalks, and the ring of teeth around each capsule mouth is split, or forked, at the tips. You need a lens to see it properly, but it is the feature that names the whole genus. The capsules hang nodding to one side, quietly echoing the sweep of the foliage below. One more habit is worth knowing: the shoots grow brittle when dry, and a cushion handled roughly sheds its tips, which happens to be one of the ways the moss spreads, since each snapped fragment can settle and grow into a fresh plant.
A favourite under glass and out of doors
Terrarium makers want Dicranum for exactly the quality that catches the eye in the wild. Set as a low mound it lends a planted jar movement and a sense of scale that flat carpet mosses never manage, and it holds its domed form for a long while in the even humidity behind glass; it features for that reason in the terrarium species roundup. As a standing, dome-forming moss it sits firmly among the acrocarps, the upright growers set against the creeping carpets in acrocarpous and pleurocarpous mosses. Out in a shaded moss garden it does the same work at a larger size, reading as soft green hummocks among the flatter feather mosses, and it is a staple of the Japanese gardens described in Japanese moss gardens.
Keeping it
Of the cushion mosses, broom fork-moss is one of the fussier to settle. It wants cool, humid, shaded, lime-free surroundings and dislikes both drying to a crisp and stewing in stagnant wet, so a spot with a little air movement suits it. Move it as whole cushions carrying their own pad of peaty substrate rather than as loose handfuls, press them into firm contact and water only with rainwater; hard tap water and its lime will sicken the plant. It spreads slowly, so treat each cushion as a specimen to place rather than a quick cover. Taking it from the wild deserves restraint, lifting small pieces only where it grows in plenty, along the lines set out in collecting moss responsibly. Given clean, damp air and shade, it repays the care with one of the most distinctive textures in the moss world.