River jelly lichen (Collema dichotomum)

River jelly lichen
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River jelly lichen fact file

River jelly lichen description


This curious species resembles seaweed more than the lichens that most of us are familiar with. It has a gelatinous appearance, is olive-green in colour, and forms circular patches on submerged rocks in upland streams.

Patch diameter: usually up to 25 mm.

River jelly lichen biology

Although this lichen is usually associated with upland or mountain streams, it does not seem to grow in areas of very fast flowing water such as rapids. It appears to tolerate some silting, but is probably sensitive to increased pollution and eutrophication - an increase in the level of nutrients in water.


River jelly lichen range

This lichen is restricted to sites in Scotland, mid Wales, the north and west of England and Northern Ireland. It is also found across northern Europe and Russia.

You can view distribution information for this species at the National Biodiversity Network Atlas.

River jelly lichen habitat

The river jelly lichen has a preference for usually silica-rich submerged rocks such as sandstone, that form slabs in partial shade. It is typically found in swift-flowing rivers, but very occasionally it also grows on submerged rocks in upland tarns.


River jelly lichen status

Classified as Vulnerable in the UK, and protected under Schedule 8 of the Wildlife and Countryside Act (1981) as amended.


River jelly lichen threats

As well as increasing nutrient levels, this species is threatened by heavy silting of the stream-beds and acidification. It may also be at risk from new hydroelectric schemes, especially the small-scale operations being planned for some upland areas.


River jelly lichen conservation

The river jelly lichen is listed in the UK Biodiversity Action Plans and included in English Nature's Species Recovery Programme. Some of the problems associated with this species are common to many other river-living plants and animals, especially the threats from pollution and increased nutrient levels through agricultural run-off. Some, however, will have a direct impact on the lichen. The increase in the number of small-scale hydroelectric schemes risks altering the ecology of many upland streams or rivers. This can have several detrimental effects, including altering the silting characteristics of the river and affecting the natural seasonal flow-rates. This lichen appears sensitive to changes in the flow of water. Riverbank management can also affect the amount of light reaching the water surface. River jelly lichen requires some shading, so clearance of too much scrub from the banks may prove detrimental. The UK BAP Species Action Plan for this lichen recommends re-introducing this species to some of its former sites, if this proves practical. In the meantime, it is important that river water quality is monitored and improved throughout the upland regions of Britain.

There may be further information about this species available via the National Biodiversity Network Atlas.
The UK Biodiversity Action Plan for this species is available at UK BAP.


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:



To become acidic.
Nutrient enrichment of aquatic or terrestrial ecosystems.



Image credit

River jelly lichen  
River jelly lichen

© Jeremy Gray

Jeremy Gray
British Lichen Society
33 Layton Lane
United Kingdom
Tel: +44 (0) 1747 850955


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