British distribution: Common around the British coasts, sometimes on very sandy soils inland.
Syntrichia ruraliformis is a very common moss on sand dunes, often colonising and carpeting the open sand surface in blowouts or amongst marram in the white dune stage, becoming locally dominant as the sand is stabilised, and persisting into the dune pasture stage. It does, however, demand at least moderate levels of calcium in the sand and it is absent from acid dunes and dune heaths.
When moist, the colonies of this moss are a conspicuous golden-yellow colour and its closely packed, erect shoots, with spreading to recurved ("squarrose-recurved"), pointed leaves, give it an almost unmistakeable appearance in the dune turf. When dry, however, shoots are twisted and shrivelled, a dull yellow-ochre brown, and the moss is hardly noticeable.
The leaf-shape is distinctive and diagnostic in this species, tapering gradually into a long, whitish hair-point. As in a number of other mosses of exposed habitats, the mass of hair-points together hold a layer of still air over the carpet or cushion surface, enabling it to conserve moisture. The tapering leaves distinguish it from the closely related S. ruralis, which occurs on old walls, stony ground, etc. inland as well as on coasts. In S. ruralis, the leaf-tip is abruptly rounded, though it has similar, projecting hair points. Generally the two species are easily distinguished, but not always so, and many prefer to regard S. ruraliformis simply as a dune subspecies, or even a variety, of S. ruralis, as indicated by the synonymy above.
The rapid response of this species to moisture changes enables it to cope with one of the significant problems of growing on sand dunes, the danger of being buried by blown sand. The untwisting of shoots can happen so rapidly that sand grains are thrown off, sometimes thrown several centimetres (Richardson, 1981). Richardson also notes that it can tolerate high temperatures at the sand surface, a temperature within a tuft of 64.5° C having been recorded.
S. ruraliformis also has the ability to make relatively rapid upward growth through sand, forming a stratified mat, binding the sand surface together and holding humus and moisture (see, e.g. Richards, in Verdoorn, 1932). While it has a relatively minor rôle in stabilisation of sand-hills, its importance in recovery from blow-outs and other damage may be significant.
S. ruraliformis is dioecious (separate male and female plants) and perhaps because colonies are commonly single clones, sporophytes are rather rare.
Photographs: (upper) Gullane, East Lothian, Scotland, March 2003; (dry-wet comparison) Longniddry Bents, East Lothian, April 2003.