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River Jelly Lichen (Collema dichotomum)

The River Jelly Lichen, scientifically known as Collema dichotomum, is a fascinating type of lichen found in aquatic environments. It is also referred to by its common name, River Jelly Lichen.

Considerations for Pets

• The thallus (lichen body) forms flattened or erect structures.

Taxonomy and Nomenclature

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

Distribution and Habitat

• This aquatic lichen grows on submerged rocks and boulders in fast-flowing water.
• It is found in the upper reaches of rivers, including those in Northumberland.
• Populations in Wales are also documented, as part of a Local Biodiversity Action Plan.
• It is known only from one record.

Morphological Characteristics

• The thallus is foliose (leafy).
• It can grow to 2-4 cm broad.
• It appears black and gelatinous when wet.
• It has broadly rounded lobes.
• Isidia and soredia are lacking.
• Spores are 4-septate, hyaline, and measure 20-40 by 3-4.5.
• Some species have one to two centimeter long, convex finger-like lobes.
• Collema dichotomum can resemble a seaweed.

Ecological Role

• It is important to "ensure canoe access does not adversely affect salmonid populations, river jelly lichen and other key species consider impact of location and timing PROJECT."

Associations

• The photobiont (the photosynthetic partner in the lichen symbiosis) is the cyanobacterium genus Nostoc.

Quirky Facts

• Some jelly lichens, when wet, absorb water until they become jelly-like.

Further Information

• More information and images can be found on ARKive.
• The Encyclopedia of Life also provides summaries and articles about Collema dichotomum.