On a shaded woodland bank, or the raw earth at the edge of a path, watch for a moss whose leaves ripple crosswise like a length of corrugated ribbon. Catch them at the right angle and the ripples flash in the light. That transverse waviness is the quickest way to fix the name of common smoothcap, one of the easier woodland mosses to learn and among the most obliging to find.
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The rippled leaf that names it
Damp, the leaves are the whole story. Each is long and strap-shaped, translucent and dark green, and crossed by a run of low undulations from one edge to the other, so a single leaf looks gently corrugated. A lens drawn along it picks out small paired teeth on the margins and a few narrow green ridges, the lamellae, standing along the midrib on the upper face. Those ridges betray its kinship: this is a relative of the haircap mosses, though it carries only a handful of them where a haircap's leaf is crowded with ridges from edge to edge. Let a patch dry and the change is startling, the leaves curling into tight, worm-like twists that all but hide the plant, until a shower or a spray of water lets them fall open again within a minute or two.
A cap without hairs
The English name turns on a deliberate comparison. As a moss ripens its spore capsule, a thin hood called the calyptra sheaths the developing lid. In the true haircaps that hood bristles with long hairs, which is exactly what gives them their name; on this moss it is very nearly bald, and the Latin Atrichum, meaning hairless, records the same feature. The capsules themselves are long, slender and a little curved, borne singly on reddish stalks and leaning over as they age, and the plant fruits generously through autumn and winter, so a colony is usually easy to confirm by its crop. To see the contrast for yourself, hold it beside the largest of its haircap relatives.
A coloniser of bare ground
Raw, disturbed earth is where this moss makes its living. It takes to shaded banks, the sides of woodland paths and rides, the spoil of a cleared ditch, the clay heaved up by a fallen tree, and the bare corners of a garden that nothing has yet grown over. It favours slightly acid to neutral soils, and it will hold loose ground that is disturbed too often for slower, mat-forming mosses to establish. The shoots stand upright in loose tufts an inch or two high rather than creeping, which places it among the acrocarps, the erect growers. Because it seizes open soil so readily, it is one of the mosses most likely to appear uninvited on a patch you have just cleared, in company with pioneers such as bonfire moss and redshank moss.
Telling it apart with confidence
At a glance, and from a little way off, a tuft can pass for a small haircap, yet the flat, wavy, see-through leaves settle it at once, since a haircap's leaves are opaque, stiffer and edged with an upright fringe of ridges. Where the foliage has crisped up in dry weather it is all too easy to stride past, so it pays to wet a doubtful patch and give it a moment for the ripples to return. The undulations, the almost smooth capsule hood and the sparse lamellae along the nerve together make this one of the more rewarding woodland mosses to key out, and a fair early success for anyone getting to grips with telling mosses apart.
In the garden and under glass
For a gardener it is a moss to welcome where it appears, since it is quietly binding bare soil against the wash of rain. It keeps out of lawns, preferring shade and disturbance to close-mown grass, so it asks for no management at all. Under glass it can be a satisfying subject, its rippled leaves and freely carried capsules offering more to look at than many small cushion mosses, provided the air stays moist enough to keep the leaves open rather than curled; the working method is laid out in the moss terrarium guide. Lifted with a thin slice of its own soil and pressed onto damp, lime-free ground, it usually settles in without complaint.