SafePlants

River Jelly Lichen (Collema dichotomum)

The River Jelly Lichen, scientifically known as Collema dichotomum, is a fascinating lichen species found in specific aquatic environments. Its unique appearance and ecological role make it an interesting subject for study and conservation.

Considerations for Pets

• This lichen grows on submerged rocks and boulders in fast-flowing water.
• It has a gelatinous texture when wet.

Considerations for Children

• This lichen grows on submerged rocks and boulders in fast-flowing water.
• It has a gelatinous texture when wet.

Taxonomy and Nomenclature

• Scientific Name: Collema dichotomum (With.) Coppins & Laundon
• Common Name: River Jelly Lichen
• Family: Collemataceae
• Order: Lecanorales
• Synonyms: Some texts refer to other Collema species, such as Collema ohioense, which may be considered synonyms depending on the source.

Description and Morphology

• The thallus (lichen body) forms flattened or erect, bright to dark green rosettes, typically between 2 to 4 cm broad.
• When wet, the thallus becomes black and gelatinous.
• It has broadly rounded lobes.
• Isidia and soredia (types of asexual propagules) are lacking.
• Spores are 4-septate (divided by 4 walls), hyaline (translucent), and measure 20-40 by 3-4.5 ?m.
• Other Collema species are described as having finger-like lobes, typically one to two centimeters long.
• One source mentions it looks more like seaweed than a lichen.

Distribution and Habitat

• The River Jelly Lichen grows on submerged rocks and boulders in fast-flowing rivers and streams.
• Specifically mentioned is its presence in the upper reaches of rivers in Northumberland, Great Britain.
• It is also found in Wales.

Ecology and Conservation

• Safeguarding existing populations requires guarding against developments such as outdoor river pursuits that might compromise its conservation.
• Canoe access should be managed to avoid adversely affecting its populations.
• Populations of the River Jelly Lichen are thought to be the largest in Great Britain in some locations.

Additional Collema species mentioned

• Collema fasciculare
• Collema crispum
• Collema auriforme
• Collema flaccidum
• Collema fragile
• Collema multipartitum
• Collema furfuraceum
• Collema nigrescens (a leafy jelly lichen found on tree bark)
• Collema tenax
• Collema coccophorum
• Collema conglomeratum
• Collema fuscovirens

Partnerships and Action Plans

• The "Partnership with Nature: A Local Biodiversity Action Plan for Wales" includes a specific River Jelly Lichen Action Plan.