Slender thread-moss (Orthodontium gracile)

SizeLength: up to 10 mm

Classified as Vulnerable in the UK. Classified as Endangered in Europe.

Slender thread-moss grows in bright green cushions, and closely resembles a much commoner species Orthodontium lineare. It requires an expert to tell them apart, but slender thread-moss has slightly narrower leaves. Mosses are difficult plants to identify, needing knowledge and a scientific field guide to be sure of which species you are looking at.

This moss has a wide world range, being found in western France, North and South America, and tropical Africa. In the UK since 1970, it has been recorded in East Sussex, Cheshire, mid-West Yorkshire and Midlothian.

In the UK, slender thread-moss grows on damp, shaded, vertical, acid rock surfaces, and sometimes in crevices. In France, it is found on sandy soil at the base of trees, and occasionally, on rotting wood. It has very occasionally been recorded on rotting wood in England.

Mosses are plants, but they belong to the lower orders. They do not produce flowers or seeds, but reproduce by spores or vegetatively. Neither do mosses have a vascular system for conveying sap, nor do they have roots to absorb water. Mosses have rhizoids, which fulfil the role of a root system in anchoring the plant to a surface. Water and nutrients are absorbed over the entire surface of the plant.

Never a common species, slender thread-moss may possibly have declined through the introduction of the similar O. lineare. Other factors may be due to changes in the microclimate or acidic water pollution.

Slender thread-moss is listed in the UK Biodiversity Action Plans (UKBAPs), and included in English Nature's Species Recovery Programme (SRP). This moss's existence may be precarious, and all the sites where it is known to occur are protected. It is also being grown ex-situ as an insurance against its loss in the wild, and trials are underway to re-introduce the species to suitable sites. As it may be threatened by an introduced species, it might be possible, under supervision, to clear competing mosses to allow slender thread-moss to re-colonise the sites. In the meantime, bryologists are being asked to pass on any records they have of this moss, to enable greater knowledge of its ecology and its true status to be gathered.

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact: