Most mosses ask for a hand lens before they will give up a name. Apple moss offers a shortcut. Where it fruits, it hangs out rows of little round capsules, each the shape and near enough the colour of an unripe crab-apple, and once you have seen them the plant is fixed in your eye for good. Bartramia pomiformis lives on shaded rock and hilly ground, and it is one of the few mosses you can put a name to from the far side of a path.
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The apples that name it
Those capsules are the whole point of the name. Each rides on a curved stalk that lifts it just clear of the cushion, and rather than the tidy urn or cylinder most mosses carry, it swells into a near-perfect sphere. Green and smooth as it ripens through late spring, it dulls to yellow-brown over summer, and as it empties and dries it puckers into furrows down one flank and leans a touch off true, so an old colony looks studded with wrinkled miniature apples. Healthy patches fruit freely, which is why a cushion in capsule is so much easier to place than a bare one. Pomiformis puts it plainly enough: apple-bearing, from the Latin pomum.
A matt, glaucous green
Out of fruit you fall back on colour and texture, and both are telling once your eye is in. The tufts are an odd dull blue-green, matt rather than glossy, closer to the bloom on a grape than to the wet shine of most woodland mosses. That flatness comes from the leaf surface, roughened all over with minute bumps, the papillae, so light scatters where a smooth leaf would glint. The leaves run long and very narrow, tapering to a fine point, and they spread into a soft star when damp before curling and crisping inward as the cushion dries. Draw one under a lens and the margins show fine teeth, with a firm nerve reaching almost to the tip. Held beside a smoother, brighter neighbour, that rough glaucous look usually settles it before the capsules confirm it.
Where it grows
This is a plant of the wetter uplands. It favours the shaded ledges and crevices of lime-poor rock, the earthy lip of a roadside cutting, stream banks and the sides of a sunken lane, anywhere the ground stays cool and damp and the stone is short of lime. In Britain it is common through Wales, the north and the west, thinner across the dry lowland east, and it fades wherever the air turns warm and the rain comes grudgingly. I have only ever met it on hillsides, tucked into a north-facing bank or a rock joint with water seeping behind it, never on a garden wall down in the flat country where I live. Its cousin the fountain apple-moss, Philonotis fontana, carries the same round capsules but haunts open, dripping flushes instead of shaded rock, so wet ground bearing apple-like fruit could be either.
A name with a botanist behind it
The genus honours John Bartram, an eighteenth-century American plantsman and one of the first serious field botanists of the colonies, though he never handled this moss himself. It is a small reminder that the Latin on a plant is as often a scrap of history as a description of the thing in front of you. A species this large in its features and this boldly marked makes a good doorway into the harder families, and it is worth practising leaf anatomy on it before you meet the fiddlier sorts covered in how to identify moss.
Better known than grown
I would talk nobody into cultivating apple moss. It belongs to cool, humid, hilly air, and in the still warmth of a lowland terrarium or on a dry garden wall it sulks and browns; the couple of tufts I carried home years ago never took, and I have left it alone since. This is a moss to know in the field, which suits it. Watch for it on your next walk through wooded hills or up a rocky lane, on a shaded bank of bare, lime-poor rock, and once the little apples have caught your eye you will begin to notice them wherever the ground lifts and the weather blows in off the west. If you want rock mosses you have a real chance of establishing, moss on rocks is the more forgiving place to begin.