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River Jelly Lichen (Collema dichotomum)

The River Jelly Lichen, scientifically known as Collema dichotomum, is a fascinating example of a lichen that thrives in aquatic environments.

Considerations for Pets

• As a lichen that can grow on rocks, be mindful of any sharp edges where pets may come into contact.

Considerations for Children

• As a lichen that can grow on rocks, be mindful of any sharp edges where children may come into contact.

Taxonomy and Nomenclature

• Scientific Name: Collema dichotomum (With.) Coppins & Laundon
• Common Name: River Jelly Lichen
• Family: Collemataceae
• Order: Lecanorales
• Synonyms: C. ohioense (for Collema Conglomeratum)

Description

• The thallus (lichen body) forms flattened or erect, bright to dark green rosettes.
• When wet, it becomes gelatinous and black in color.
• The thallus is foliose (leafy), reaching up to 2-4 cm broad.
• Lobes are broadly rounded.
• Spores are 4-septate, hyaline, and measure 20-40 by 3-4.5.

Distribution and Habitat

• The River Jelly Lichen is found in the upper reaches of rivers in areas such as Northumberland.
• It grows on submerged rocks and boulders in fast-flowing water.
• It is also found in Wales and the river populations of both the rare whorled solomon&#39s-seal and the river jelly lichen are thought to be the largest in Great Britain.

Ecology

• This lichen is a cyanolichen, meaning its photobiont is a cyanobacterium, specifically from the genus Nostoc.

Quirky Facts

• Collema dichotomum is sometimes said to resemble seaweed more than a typical lichen.
• Some jelly lichens absorb water until they are jelly-like when it rains.

Additional Information

• The Encyclopedia of Life offers a summary of Collema dichotomum.
• ARKive provides photos and facts about the River Jelly Lichen.