Latin name: Orthodontium gracile
Slender thread-moss is rare and usually occurs on well-drained outcrops of acidic sandstone in humid locations. In 1999 it was re-discovered at the Strid on the Bolton Abbey Estate in Wharfedale. It had last been seen there in 1954.This site also holds the only known record of Slender thread-moss occurring on wood.
Slender thread-moss is similar to the more common Cape thread-moss however the former has dull, silky, light green leaves, but has a pale, smooth capsule when mature and empty. Its UK stronghold is in Cheshire and Staffordshire with other scattered records in South Devon, East Sussex, Mid West Yorkshire, Westmorland, Cumberland, the Cheviots, the Central belt of Scotland and the West of Northern Ireland.
In the Yorkshire Dales National Park the species is known only to the Bolton Abbey Estate near the Strid waterfalls. Members of the Yorkshire Dales Biodiversity Forum, the British Bryological Society and other local naturalists are planning further surveys to aid the conservation of this species.
The slender thread-moss is a nationally rare bryophyte, its status on the threatened bryophyte database is Vulnerable, and consequently it is a UKBAP priority species. This moss may be sensitive to specific air pollutants which is a possible cause of its decline in the second half of the twentieth century.