Kneel by a shaded bank on limestone in the right part of the country and you may find what looks like a scatter of tiny green flowers pressed to the ground. Each is a spreading rosette of broad leaves on a short reddish stalk, and the whole thing reads far more like a small succulent or an opening bloom than anyone's first idea of a moss. This is rose moss (Rhodobryum roseum), and the shape gives it away before you have looked at anything else.
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A rosette like an open flower
Most mosses carry their leaves fairly evenly up the stem. Rose moss gathers its largest leaves into a single flat rosette at the very tip of an upright shoot, so a well-grown plant looks like a green star or a small open rose an inch or so across. The stem below stays bare and reddish, clothed only in minute scale-leaves, which perches the rosette on a little stalk like a palm tree in miniature. Those rosette leaves are large by mossy standards, oblong and tongue-shaped, tapered at the base and widening to a rounded, toothed tip, with a firm nerve running most of their length and a clear border of narrow cells round the edge. Wet a dried plant and the leaves spread again within moments, opening the rosette back into its flower shape.
The stems you do not see
What holds a colony together runs out of sight. Rose moss spreads by horizontal underground stems, pale and nearly leafless, that creep through the leaf litter and soil and push up the leafy rosettes here and there along their length. A patch is often a loose scatter of single rosettes rather than a tight cushion, each one joined to its neighbours below ground. That underground habit matters, because the moss rarely fruits in Britain. When capsules do come they hang on a red stalk in the way of its relatives in the Bryaceae, but most colonies you meet are getting along quietly by those creeping stems and by broken-off fragments instead of by spores, which is part of why the moss stays so local.
Where to look for it
Shade and lime are what it asks for. It wants humus-rich, base-rich ground out of direct sun: the floor of an ash or beech wood over limestone, a shaded grassy bank, ledges and turf on chalk or basic rock, now and then among the grass of an old calcareous meadow. Strongly acid peat and heath do not suit it, so a sour moor is the wrong place to search. Across Britain and Ireland it is thinly and locally distributed, commoner where the rock is calcareous and largely missing from the acid lowlands, and nowhere is it a moss you trip over. I have found it just once with any confidence, a few rosettes on a mossy limestone ledge in dappled shade, and the memory of that small green rose has kept me peering at every limy bank since.
Telling it from the thyme-mosses
The broad-leaved thyme-mosses can cause a moment's doubt, since they too carry large, bordered, toothed leaves. Their arrangement is the giveaway. A thyme-moss such as swan's-neck thyme-moss (Mnium hornum) or hart's-tongue thyme-moss (Plagiomnium undulatum) ranks its leaves all the way up the shoot, so the stem looks leafy from top to bottom; rose moss bundles them into that one rosette above a bare stalk. If you meet a rose moss with an unusually full, flat rosette of many leaves in a strongly calcareous spot, its scarcer relative Rhodobryum ontariense is worth a thought, though telling the two apart properly is a job for a key and a microscope. Working out any moss by its growth form before anything else is a habit worth building, and how to identify moss walks through it; the two thyme-mosses have profiles of their own under swan's-neck thyme-moss and hart's-tongue thyme-moss.
The name, and leaving it be
Rhodobryum means simply the rose moss, from the Greek for a rose and the flat, spreading rosette that earns the comparison, so the Latin and the English land on the same picture. Its rosettes are one of the stock examples people reach for when they wonder whether mosses flower, a question taken up under do mosses flower, and the short of it is that the rose is all leaves and no bloom. Because it is uncommon, slow, and easily lost when its wood or bank is cleared or drained, this is not a moss to lift for a terrarium or a bowl. Admire it, photograph it if you like, and leave the rosettes to travel by their hidden stems as they always have.