The irregular branches of this beautiful, golden-yellow pleurocarpous moss, with its gracefully curving, pleated, hooked leaves, are a real show-stopper, even for those who are usually impressed only by more blousy vascular plants. Unfortunately, however, it is very restricted in both its geographical range and its habitat requirements in Britain. To see it, you need to be in the very north-east of the country: Shetland (where it is widespread), Orkney, and coastal regions of north-east mainland Scotland…or St. Kilda, if you are lucky enough to get there. Its favourite spot is well-drained, lightly grazed turf, on cliff tops right by the sea.
So, what might you confuse it with? The hooked, pleated leaves and golden colour will of course be the first things to catch your eye. Hypnum cupressiforme var. lacunosum can look pretty hearty and a lovely golden colour, but the leaves have no nerve and are not pleated. Most other things that look similar, with hooked leaves, such as Drepanocladus, Scorpidium, Sarmentypnum and Warnstorfia species grow in wet places and their leaves are not pleated. (The leaves of Sarmentypnum exannulatum can sometimes appear a little pleated, but the habitat and really obvious clear patches of alar cells, when a few leaves are pulled off will avoid confusion.) Palustriellas do have pleated leaves, but again grow in wet places and, with care and a judicious scrape of the stem with a thumbnail, will display tiny leaf-like paraphyllia, making the stem look fuzzy. Hamatocaulis vernicosus grows in wet places, the leaves are not as long and narrow, and they have a reddish base.
The most likely source of confusion is with its congener S. uncinata. This can be puzzling. Many of the habitats occupied by S. uncinata, such as wet woodland, montane cliffs and stream edges rule out S. orthothecioides. However, in Shetland, for example, both species can grow near each other, in turf by the sea. The knitted brow of confusion can be smoothed by the presence of capsules, which are commonly produced in S. uncinata, very rarely in Britain in S. orthothecioides. Otherwise, it is probably best to confirm the difference microscopically, with help from the article by David Long in J. Bryol. 17, 111 – 117, (1992). S. orthothecioides is usually more robust and not as regularly pinnately branched. The leaves of S. orthothecioides are broader relative to their length, the cells above the alar cells in a larger group and sometimes porose. In the lower part of the stem leaf, the nerve of S. orthothecioides lies in a deep narrow fold, so it is quite hard to see, even under the microscope, whereas that of S. uncinata is clearly visible near the base. This is apparently evident in leaf sections, but such sections often distort under the cover slip and it can be frustrating. Just looking at a number of stem leaves under low magnification will tell the story.
On a sunny day in Shetland, strolling along a cliff top by a crystal sea and finding a good patch of this delightful moss is a real pleasure – time to sit down and enjoy a coffee and an energy bar.Read the Field Guide account