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Slender Thread-moss Slender Thread-moss Credit: Robert Goodison

Rare Mosses in the Dales

yorkshire-feather-moss

Yorkshire Feather-moss

Thamnobryum cataractarum

Thamnobryaceae

This species of aquatic moss was new to science in 1991. It was discovered by bryologists Hodgetts and Blockeel on gritstone rock in a deep ravine near Ingleton in the Yorkshire Dales National Park. Research has shown that it is most closely related to Thamnobryum fernandesii, a moss that is endemic to Madeira.

Due to its rarity, Yorkshire feather moss is a UKBAP priority species and on the nature in the Dales 2020 Vision: the second biodiversity action plan for the Yorkshire Dales National Park. 

incurved-feather-moss

Incurved Feather-moss

Homonallium incurvatum

Order: Hypnales

Incurved feather-moss is a moss of moderately shaded, base-rich rocks in humid but not wet environments. This species appears to prefer growing close to ground level amongst sparse vegetation, sometimes on rocks in drystone walls, in woodland or occasionally on rocky crag ledges.

This nationally rare species has its stronghold in northern England. A significant proportion of the known UK population of this moss occurs in the Yorkshire Dales National Park on walls and boulders on woodland edges. There are historical records for six areas in the Yorkshire Dales National Park including Ingleton, Ingleborough and Austwick in the South West of the Park and Askrigg, Aysgarth and East Witton in Wensleydale in the North East of the Park.

nowells-limestone-moss

Nowell’s Limestone Moss

Zygodon gracilis

Family: Orthotrichaceae

Nowell’s limestone moss is a very rare species that is only known from four areas in Britain which are all within the Craven Limestone area of the Yorkshire Dales National Park. Although originally found growing on scree slopes, the few surviving populations are found on a stretches of dry stone wall in the Pen-y-ghent area of the National Park.

This species is named after John Nowell, a local bryologist who first discovered the moss in 1860. Nowell’s limestone moss is a dioicous moss, meaning that there are separate male and female plants. The moss will only sexually reproduce where climatic conditions are right and male and female plants are within 20 cm of each other. In addition the moss can reproduce vegetatively, where new plants are propagated from vegetative tissues only; this method of reproduction means that the moss will never colonise any new sites. One of the main reasons for the rarity of Nowell’s Limestone Moss is that the males and females plants were thought to be too far apart to reproduce. This is highlighted by the fact that until relatively recently, the last person to find the moss in capsule, or fruiting, was John Nowell in 1866.

In 2003 surveyors from the University of Bradford and Natural History Museum in London undertook detailed survey work to accurately plot the location of all populations of this moss at its historical sites on the slopes of Pen-y-ghent. Just over 500 clumps of Nowell’s Limestone moss were recorded and approximately 70% of the plants found were female. The surveyors were delighted to find one fruiting body. This was the first time that this species had been witnessed ‘in capsule’ for nearly 140 years.

Now that the distribution of the species has been accurately mapped, any dry stone walling work in this area can be undertaken sympathetically to ensure that the survival of this endemic species is not put at risk.

slender-thread-moss

Slender Thread-moss

Orthodontium gracile

Family: Bryales

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.