Some mosses look like nothing but moss; tamarisk moss looks like a fern that has been left out in the rain and shrunk in the wash. Across the floor of a damp wood it spreads in loose green wefts, each shoot opening into a flat, branched frond no longer than a finger. At ground level it is about the most graceful thing a temperate woodland has to show.
A fern cut down to size
Thuidium tamariscinum builds its shoots like little trees. From a dark, almost blackish creeping stem rise repeatedly divided fronds, the side branches themselves branching again and then once more, so the whole spray comes out two or three times pinnate and lies as flat as a pressed fern leaf. The colour is a deep, faintly yellowish green, and the fronds arch and overlap into a soft, springy weft instead of pressing tight to the soil. At arm's length a patch could pass for a colony of tiny bracken, and close up the likeness only sharpens, which is why the name fern moss clings to it as readily as the bookish tamarisk.
The fuzz on the stem
Lift a single shoot and run a lens along the main stem. It is clothed in a felt of minute green threads, the paraphyllia, branched filaments scattered so thickly that the stem looks faintly woolly. Few mosses carry them in such quantity, and they make a useful confirmation when a young frond has not yet opened out enough to show its full pattern. The plant fruits only now and then, raising curved capsules on long red stalks, so for most of the year the frond and the fuzz are how you will know it. Creeping and freely branching, it belongs among the pleurocarps, the trailing growers set against the upright cushion mosses in acrocarpous and pleurocarpous mosses.
Where it grows
This is a plant of shade and of ground with a little body to it. It favours neutral to base-rich woodland floors, the cool, humus-rich earth under ash, hazel and oak on heavier soils, and it runs over shaded banks, the sides of ditches and the bottoms of old hedges. Where the acid-loving bun moss and broom fork-moss insist on sour peat, tamarisk moss takes a milder, even slightly limey soil quite happily, though it will have nothing to do with a baking open wall. Given the damp shade it wants, it can sheet across a wide stretch of woodland floor, threaded through the leaf litter among the flatter feather mosses.
In the moss garden and under glass
Little else brings such movement to a planting. The arching fern fronds register at a glance as a wholly different texture from the flat carpets and tight domes around them, so a drift of tamarisk moss lends a moss garden or a shaded border the air of a miniature woodland floor; it is a mainstay of the plantings described in Japanese moss gardens and a rewarding choice where you want living ground cover with genuine character. Behind glass it plays the part of the fern in a terrarium, set as a tall accent above lower mosses, so long as the case stays cool, humid and out of direct sun. In a hot, dry room it soon looks tired and thin.
Keeping it
Patience suits this moss better than fussing. Give it steady shade, humid air and soil that never bakes, water it with rainwater, and leave it largely to itself once it has knitted down. It travels best as whole wefts carrying a little of their own leaf-mould rather than as pulled-apart strands, laid on firm damp ground and pressed gently so the undersides make contact. It settles more slowly than the toughest carpet mosses and dislikes both drought and stagnant wet, so a shaded spot with a breath of moving air goes a long way. Should you gather it from the wild, take small pieces only where it grows in plenty and leave any thin or struggling patch alone, in the spirit set out under collecting moss responsibly.