SafePlants

River Jelly Lichen (Collema dichotomum)

The River Jelly Lichen, scientifically known as Collema dichotomum, is a fascinating lichen species that resembles seaweed more than a typical lichen. Its common name aptly describes its jelly-like consistency when wet and its association with rivers.

Considerations for Pets

• This lichen grows on submerged rocks and boulders, so may be found in areas where pets can access water.
• The thallus is gelatinous when wet.

Considerations for Children

• This lichen grows on submerged rocks and boulders, so may be found in areas where children can access water.
• The thallus is gelatinous when wet.

Taxonomy and Nomenclature

• Scientific Name: Collema dichotomum (With.) Coppins &amp Laundon
• Common Name: River Jelly Lichen
• Family: Collemataceae
• Order: Lecanorales
• Taxon Version Key: NBNSYS0000018437

Distribution and Habitat

• The River Jelly Lichen is found in the upper reaches of rivers, growing on submerged rocks and boulders in fast-flowing water.
• It is known from at least one location in Northumberland and is the subject of a Local Biodiversity Action Plan in Wales.
• The populations of river jelly lichen are thought to be the largest in Great Britain.

Morphological Characteristics

• The thallus (lichen body) is foliose (leafy) and can grow to 2-4 cm broad.
• It has a black, gelatinous texture when wet.
• The lobes are broadly rounded.
• Isidia and soredia are lacking.
• Spores are 4-septate, hyaline, and measure 20-40 by 3-4.5 ?m.

Ecological Role

• Conservation efforts are in place to safeguard existing populations, protecting them from developments that might compromise their survival, such as outdoor river pursuits.

Interactions with Other Organisms

• The photobiont partner in Collema lichens is the cyanobacterium genus Nostoc.

Further Information

• Learn more about the River Jelly Lichen on ARKive.
• Encyclopedia of Life includes summaries and articles about Collema dichotomum.